Herd immunity in adults against influenza-related illnesses with use of the trivalent-live attenuated influenza vaccine (CAIV-T) in children

Decreased risk of non-influenza respiratory infection after influenza B virus infection in children

Previous studies suggest that influenza virus infection may provide temporary non-specific immunity and hence lower the risk of non-influenza respiratory virus infection. In a randomized controlled trial of influenza vaccination, 1 330 children were followed-up in 2009-2011. Respiratory swabs were collected when they reported acute respiratory illness and tested against influenza and other respiratory viruses. We used Poisson regression to compare the incidence of non-influenza respiratory virus infection before and after influenza virus infection. Based on 52 children with influenza B virus infection, the incidence rate ratio (IRR) of non-influenza respiratory virus infection after influenza virus infection was 0.47 (95% confidence interval: 0.27-0.82) compared with before infection. Simulation suggested that this IRR was 0.87 if the temporary protection did not exist. We identified a decreased risk of non-influenza respiratory virus infection after influenza B virus infection in children. Further investigation is needed to determine if this decreased risk could be attributed to temporary non-specific immunity acquired from influenza virus infection.

Epidemiology and Burden of Influenza in Children 0-14 Years Over Ten Consecutive Seasons in Italy

BACKGROUND

In Europe, influenza vaccination coverage in the pediatric population is low. This study describes the influenza incidence and associated healthcare utilization in the pediatric population in Italy.

METHODS

Deidentified data from electronic medical records for children 0-14 years old seen by >150 family pediatricians in the Pedianet network in Italy were evaluated for 10 influenza seasons spanning 2010-2020. Incidence of influenza (cases per 1000 person-months), related sequelae and associated healthcare resource use were determined using diagnostic, prescription and medical examination data.

RESULTS

Over 10 seasons, an average of 8892 influenza cases (range, 4700-12,419; total 88,921) were diagnosed in a cohort of 1,432,384 children 0-14 years of age. Influenza vaccination coverage was 3.6% among children with an influenza diagnosis and 6.8% among children without. Influenza-related healthcare resource utilization included 1.58 family pediatrician visits per influenza episode and 220 ED and 111 hospital admissions, with the highest resource usage among children 1-4 years and lowest among children <6 months old. The most common influenza complications were acute otitis media (2.9% of influenza cases) and pneumonia (0.5%). Antibiotics were prescribed in 38.7% of influenza cases; no antiviral agents were prescribed. One intensive care unit admission and 2 cases requiring ventilatory support were documented. No influenza-related deaths were reported.

CONCLUSION

Pediatric influenza vaccination was low despite the burden and healthcare use related to seasonal influenza in the pediatric population during a 10-year period in Italy.

Vaccine Effectiveness of Cell-Based Quadrivalent Influenza Vaccine in Children: A Narrative Review

Cell-based manufacturing of seasonal influenza vaccines eliminates the risk of egg-adaptation of candidate vaccine viruses, potentially increasing vaccine effectiveness (VE). We present an overview of published data reporting the VE and cost-effectiveness of a cell-based quadrivalent influenza vaccine (QIVc) in preventing influenza-related outcomes in the pediatric population. We identified 16 clinical studies that included data on the VE of a QIVc or the relative VE (rVE) of a QIVc versus an egg-based QIV (QIVe) in children and/or adolescents, 11 of which presented estimates specifically for the pediatric age group. Of these, two studies reported rVE against hospitalizations. Point estimates of rVE varied from 2.1% to 33.0%, with studies reporting significant benefits of using a QIVc against influenza-related, pneumonia, asthma, and all-cause hospitalization. Four studies reported rVE against influenza-related medical encounters, with point estimates against non-strain specific encounters ranging from 3.9% to 18.8% across seasons. One study evaluated rVE against any influenza, with variable results by strain. The other four studies presented VE data against laboratory-confirmed influenza. Three health economics studies focusing on a pediatric population also found the use of QIVc to be cost-effective or cost-saving. Overall, using a QIVc is effective in pediatric patients, with evidence of incremental benefits over using a QIVe in preventing hospitalizations and influenza-related medical encounters in nearly all published studies.

Indirect Protection from Vaccinating Children against Influenza A Virus Infection in Households

Influenza vaccination is an important intervention to prevent influenza virus infection. Our previous analysis suggested that indirect protection is limited in an influenza B epidemic in Hong Kong. We further analyzed six influenza A epidemics to determine such potential. We applied a statistical model to estimate household transmission dynamics in the 3 influenza A(H3N2) and 3 pandemic influenza A(H1N1) epidemics. Then, we estimated the reduction in infection risk among unvaccinated household members when all children in households are vaccinated, with different assumptions on vaccine efficacy (VE). In the optimal scenario that VE was 70%, the reduction to the total probability of infection was only marginal, with relative probabilities ranged from 0.91–0.94 when all children in households were vaccinated because community was by far the main source of infection during the six epidemics in our study. The proportion of cases attributed to household transmission was 10% (95% CrI: 7%, 13%). Individual influenza vaccination is important even when other household members are vaccinated, given the degree of indirect protection is small.

Cost-Effectiveness of Intranasal Live-Attenuated Influenza Vaccine for Children: A Systematic Review

Introduction: The public health burden of seasonal influenza is significant, and influenza vaccination is the most effective preventive strategy. Nonetheless, the recommendation of influenza immunization in the pediatric population is still underrepresented. Our work aimed to assess the cost-effectiveness of pediatric influenza vaccination with the intranasal live-attenuated influenza vaccine (LAIV). Methods: We performed a systematic review of publications from PubMed/MEDLINE, Embase, and Scopus, covering the period from 1 January 2000 to 30 April 2022. We searched for economic evaluations that studied the impacts of LAIV among children or the pediatric population. Studies that considered incremental cost-effectiveness ratios (ICERs), in terms of cost per gain in life years, quality adjusted life years, or disability-adjusted life years, were covered. The Consensus Health Economic Criteria (CHEC) Extended Checklist was adopted to check the quality of the included studies. Results: Thirteen studies were included for the final review that were of good or excellent quality. The implementation of influenza vaccination with intranasal LAIV in the pediatric population was cost-effective when compared to the immunization strategies for the elderly and the high-risk groups alone or with no vaccination. The efficacy of LAIV for children, vaccination coverage, and the vaccine price were significant factors to the cost-effectiveness of influenza vaccination for children. Another significant contribution to the cost-effectiveness was the herd immunity arising from pediatric immunization against influenza. Conclusions: The implementation of influenza vaccination in the pediatric population with LAIV is cost-effective. Policymakers and health authorities may consider the evidence on the development of the pediatric influenza vaccination in their immunization schedules.

Relative Effectiveness of Cell-based Versus Egg-based Quadrivalent Influenza Vaccines in Children and Adolescents in the United States During the 2019-2020 Influenza Season

BACKGROUND

Egg-based influenza vaccine production can lead to the accumulation of mutations that affect antigenicity. The mammalian cell-based inactivated quadrivalent influenza vaccine (IIV4c) may improve effectiveness compared with egg-based vaccines. This study estimated the relative vaccine effectiveness (rVE) of IIV4c versus egg-based inactivated quadrivalent influenza vaccine (IIV4e) in preventing influenza-related medical encounters (IRME) among children and adolescents during the 2019-2020 US influenza season.

METHODS

This retrospective cohort study used a dataset linking primary and specialty care electronic medical records with medical and pharmacy claims data from US residents 4 through 17 years of age vaccinated with IIV4c or IIV4e during the 2019-2020 influenza season. Odds ratios (ORs) were derived from a doubly robust inverse probability of treatment-weighted approach adjusting for age, sex, race, ethnicity, region, index week, health status and two proxy variables for healthcare accessibility and use. Adjusted rVE was estimated by (1-OR adjusted )*100, and an exploratory analysis evaluated IRMEs separately for outpatient and inpatient settings.

RESULTS

The final study cohort included 60,480 (IIV4c) and 1,240,990 (IIV4e) vaccine recipients. Fewer IRMEs were reported in subjects vaccinated with IIV4c than IIV4e. The rVE for IIV4c versus IIV4e was 12.2% [95% confidence interval (CI): 7.5-16.6] for any IRME and 14.3% (9.3-19.0) for outpatient IRMEs. Inpatient IRMEs were much less frequent, and effectiveness estimates were around the null.

CONCLUSIONS

Fewer IRMEs occurred in pediatric subjects vaccinated with IIV4c versus IIV4e. These results support the greater effectiveness of IIV4c over IIV4e in this population during the 2019-2020 US influenza season.

SARS-CoV-2 transmission across age groups in France and implications for control

The shielding of older individuals has been proposed to limit COVID-19 hospitalizations while relaxing general social distancing in the absence of vaccines. Evaluating such approaches requires a deep understanding of transmission dynamics across ages. Here, we use detailed age-specific case and hospitalization data to model the rebound in the French epidemic in summer 2020, characterize age-specific transmission dynamics and critically evaluate different age-targeted intervention measures in the absence of vaccines. We find that while the rebound started in young adults, it reached individuals aged ≥80 y.o. after 4 weeks, despite substantial contact reductions, indicating substantial transmission flows across ages. We derive the contribution of each age group to transmission. While shielding older individuals reduces mortality, it is insufficient to allow major relaxations of social distancing. When the epidemic remains manageable (R close to 1), targeting those most contributing to transmission is better than shielding at-risk individuals. Pandemic control requires an effort from all age groups.

[Analysis of the changes and characteristics of pediatric outpatient visits in a general hospital in Beijing before and after the COVID-19 pandemic]

OBJECTIVE

To analyze the changes and characteristics of pediatric outpatient visits in a general hospital before and after the coronavirus disease (COVID-19) epidemic.

METHODS

Based on the registration data of pediatric outpatient visits in the information system (HIS)of Beijing Tsinghua Changgung Hospital, from January 1 2018 to December 31 2020, aged 0 to 16 years, we analyzed the changes of outpatient visits before and after the epidemic, focusing on respiratory infection including influenza. The relationship between the outpatient visits and age and quarterly distribution were also studied.

RESULTS

(1) Respiratory infection accounted for the majority of outpatient visits in 2018 and 2019 (60.6% and 60.5%, respectively). Non-respiratory infection accounted for the main proportion of outpatient visits in 2020, while respiratory infection accounted for only 47.4%. Annual respiratory infection visits, respiratory infectious diseases visits especially influenza visits all decreased significantly in 2020 compared with that in 2018 and 2019 (P < 0.05). (2)Respiratory infection visits were highest in the infant group, lowest in the school age group (P < 0.05) and highest in the fourth quarter each year. It decreased significantly in the second quarter of 2020 with statistical significance when compared with the other quarters of 2020(P < 0.05). (3)Influenza accounted for the highest proportion of respiratory infectious diseases visits in each year. It was highest in first quarter, which was significantly different from the other quarters of the year (P < 0.05). There were different distributions of influenza visits throughout 2018 and 2019, while it was only distributed in the first quarter and 99% in January in 2020.

CONCLUSION

The respiratory infection and influenza visits have decreased significantly in our pediatric outpatient department after the COVID-19 epidemic, which is considered closely related to the lifestyle and personal protection after the epidemic. It is recommended that health education on respiratory infection and influenza prevention should be strengthened, especially in winter and spring, to promote the development of good respiratory and hand hygiene habits.

City-wide school-located influenza vaccination: A retrospective cohort study

BACKGROUND

We measured the effectiveness of a city-wide school-located influenza vaccination (SLIV) program implemented in over 102 elementary schools in Oakland, California.

METHODS

We conducted a retrospective cohort study among Kaiser Permanente Northern California (KPNC) members of all ages residing in either the intervention or a multivariate-matched comparison site from September 2011 - August 2017. Outcomes included medically attended acute respiratory illness (MAARI), influenza hospitalization, and Oseltamivir prescriptions. We estimated difference-in-differences (DIDs) in 2014-15, 2015-16, and 2016-17 using generalized linear models and adjusted for race, ethnicity, age, sex, health plan, and language.

RESULTS

Pre-intervention member characteristics were similar between sites. The proportion of KPNC members vaccinated for influenza by KPNC or the SLIV program was 8-11% higher in the intervention site than the comparison site during the intervention period. Among school-aged children, SLIV was associated with lower Oseltamivir prescriptions per 1,000 (DIDs: -3.5 (95% CI -5.5, -1.5) in 2015-16; -4.0 (95% CI -6.5, -1.6) in 2016-17) but not with other outcomes. SLIV was associated with lower MAARI per 1,000 in adults 65 + years (2014-15: -13.2, 95% CI -23.2, -3.2; 2015-16: -21.5, 95% CI -31.1, -11.9; 2016-17: -13.0, 95% CI -23.2, -2.9). There were few significant associations with other outcomes among adults.

CONCLUSIONS

A city-wide SLIV intervention was associated with higher influenza vaccination coverage, lower Oseltamivir prescriptions in school-aged children, and lower MAARI among people over 65 years, suggesting possible indirect effects of SLIV among older adults.

Warp Speed for Coronavirus Disease 2019 (COVID-19) Vaccines: Why Are Children Stuck in Neutral?

While adult clinical trials of coronavirus disease 2019 (COVID-19) vaccines have moved quickly into phase 3 clinical trials, clinical trials have not started in children in the United States. The direct COVID-19 impact upon children is greater than that observed for a number of other pathogens for which we now have effective pediatric vaccines. Additionally, the role of children in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission has clearly been underappreciated. Carefully conducted phase 2 clinical trials can adequately address potential COVID-19 vaccine safety concerns. Delaying phase 2 vaccine clinical trials in children will delay our recovery from COVID-19 and unnecessarily prolong its impact upon children's education, health, and emotional well-being, and equitable access to opportunities for development and social success. Given the potential direct and indirect benefits of pediatric vaccination, implementation of phase 2 clinical trials for COVID-19 vaccines should begin now.

Prevalence of SARS-CoV-2 Infection in Children and Their Parents in Southwest Germany

Importance

School and daycare closures were enforced as measures to confine the novel coronavirus disease 2019 (COVID-19) pandemic, based on the assumption that young children may play a key role in severe acute respiratory coronavirus 2 (SARS-CoV-2) spread. Given the grave consequences of contact restrictions for children, a better understanding of their contribution to the COVID-19 pandemic is of great importance.

Objective

To describe the rate of SARS-CoV-2 infections and the seroprevalence of SARS-CoV-2 antibodies in children aged 1 to 10 years, compared with a corresponding parent of each child, in a population-based sample.

Design, Setting, and Participants

This large-scale, multicenter, cross-sectional investigation (the COVID-19 BaWü study) enrolled children aged 1 to 10 years and a corresponding parent between April 22 and May 15, 2020, in southwest Germany.

Exposures

Potential exposure to SARS-CoV-2.

Main Outcomes and Measures

The main outcomes were infection and seroprevalence of SARS-CoV-2. Participants were tested for SARS-CoV-2 RNA from nasopharyngeal swabs by reverse transcription-polymerase chain reaction and SARS-CoV-2 specific IgG antibodies in serum by enzyme-linked immunosorbent assays and immunofluorescence tests. Discordant results were clarified by electrochemiluminescence immunoassays, a second enzyme-linked immunosorbent assay, or an in-house Luminex-based assay.

Results

This study included 4964 participants: 2482 children (median age, 6 [range, 1-10] years; 1265 boys [51.0%]) and 2482 parents (median age, 40 [range, 23-66] years; 615 men [24.8%]). Two participants (0.04%) tested positive for SARS-CoV-2 RNA. The estimated SARS-CoV-2 seroprevalence was low in parents (1.8% [95% CI, 1.2-2.4%]) and 3-fold lower in children (0.6% [95% CI, 0.3-1.0%]). Among 56 families with at least 1 child or parent with seropositivity, the combination of a parent with seropositivity and a corresponding child with seronegativity was 4.3 (95% CI, 1.19-15.52) times higher than the combination of a parent who was seronegative and a corresponding child with seropositivity. We observed virus-neutralizing activity for 66 of 70 IgG-positive serum samples (94.3%).

Conclusions and Relevance

In this cross-sectional study, the spread of SARS-CoV-2 infection during a period of lockdown in southwest Germany was particularly low in children aged 1 to 10 years. Accordingly, it is unlikely that children have boosted the pandemic. This SARS-CoV-2 prevalence study, which appears to be the largest focusing on children, is instructive for how ad hoc mass testing provides the basis for rational political decision-making in a pandemic.

Cost-effectiveness of childhood influenza vaccination in Europe: results from a systematic review

Introduction: Influenza can be a significant public health problem. Nevertheless, it is preventable through vaccination. Concerning the pediatric population, the recommendation of influenza vaccination is under-represented in many European countries. The aim of this systematic review is to evaluate the cost-effectiveness of universal childhood vaccination against influenza in Europe.Areas covered: We conducted a systematic review of original article assessing the cost-effectiveness of influenza vaccination by searching PubMed, Embase and Scopus databases for studies in English, starting from January 1^st, 2010 up to October 21^st, 2020.Expert opinion: Our literature review showed that all studies identified highlight that pediatric vaccinations using a live vaccine, especially in the quadrivalent formulation, are cost-effective compared to current vaccinations (elderly and at-risk groups) with TIV or no vaccination. A significant contribution to this positive economic profile is due to the indirect protection. Already many clinical data report the relevant direct and indirect impact of vaccination against influenza for younger subjects. The recent studies collected in this review showed also that the pediatric vaccination is also cost-effective. Therefore, decision-makers should now consider this new favorable evidence.

Population Mortality and Laws Encouraging Influenza Vaccination for Hospital Workers

BACKGROUND

Since 1995, 14 states have passed laws encouraging or mandating influenza vaccination for hospital workers. Although the Centers for Disease Control and Prevention recommends vaccinating health care workers to reduce disease transmission and patient risk, the effect of these laws on pneumonia and influenza mortality is unknown.

OBJECTIVE

To measure the effect of state-level hospital worker influenza vaccination laws on pneumonia and influenza mortality.

DESIGN

Quasi-experimental observational study.

SETTING

United States.

PARTICIPANTS

Population of all states from 1995 to 2017.

INTERVENTION

State adoption of a law promoting influenza vaccination for hospital workers.

MEASUREMENTS

Pneumonia and influenza mortality per 100 000 persons by state and by month, both population-wide and separately by age group, obtained from restricted-access National Vital Statistics System files. Linear and log-linear models were used to compare changes in mortality rates for adopting versus nonadopting states.

RESULTS

Implementation of state laws requiring hospitals to offer influenza vaccination to their employees was associated with a 2.5% reduction in the monthly pneumonia and influenza mortality rate (-0.16 deaths per 100 000 persons [95% CI, -0.29 to -0.02]; P = 0.022) during the years when the vaccine was well matched to the circulating strains. The largest effects occurred among elderly persons and during peak influenza months.

LIMITATION

Utilization of large-scale national data precluded analysis of more specific outcomes, such as laboratory-confirmed or hospital-acquired influenza.

CONCLUSION

State laws promoting hospital worker vaccination against influenza may be effective in preventing pneumonia- and influenza-related deaths, particularly among elderly persons. Vaccinating hospital workers may substantially reduce the spread of influenza and protect the most vulnerable populations.

PRIMARY FUNDING SOURCE

None.

Effectiveness of influenza vaccination in infants and toddlers with and without prior infection history: The Japan Environment and Children's Study

We calculated the Poisson-regression-adjusted relative risk (RR) of new influenza infection by vaccination, prior infection, and vaccination after prior infection in a large Japanese birth cohort, using data from ≤89,253 children aged 6 months to 3 years. The effectiveness of risk reduction (1 - RR) by vaccination at ages 1.5-3 years was 21%-31%. The RR of new infection after prior infection vs. no prior infection was 2.58-19.3 at age 1-3 years. An analysis of the 1 - RR data stratified by having at least one senior sibling and/or attending nursery school revealed that vaccination reduced the RR by 22%-40%. The 1 - RR of new infection was 21% in 3-year-old children who were vaccinated after prior infection. All these findings are statistically significant. The results consistently indicate that, regardless of having at least one senior sibling, attending nursery school, and/or being previously infected with influenza, infants and toddlers will benefit from influenza vaccination.

Recommendations for influenza vaccination in burns patients based on a systematic review of the evidence

Severe burn injury is a serious systemic insult that can lead to life threatening secondary infections. Immunosuppression, inhalation injury and prolonged length of hospital stay are factors which predispose patients to severe respiratory tract infections. Furthermore, evidence shows that burns can put one at risk of infection long after the original injury. Currently in the United Kingdom, the annual National Flu Immunisation programme outlines guidance for groups who are deemed high risk and therefore eligible for the influenza vaccine. At present, no guidance exists for administration of the influenza vaccine in burn injured patients, despite knowledge of immunosuppression. The aim of this literature review is to examine the evidence for associations between burn injury and influenza and where available, evaluate efficacy of influenza vaccines in this cohort. In addition, literature was searched for the effectiveness of the influenza vaccine in patients 65 years and above, and in patients admitted to the intensive care unit (ICU); two domains common to patients with severe burns. Three papers were found to suggest increased susceptibility to influenza following burn injury, however no papers studying the effectiveness of the influenza vaccine in this group were found. Several studies demonstrated improved outcomes in patients over 65 years and patients admitted to ICU. Following evaluation of the evidence, this review advocates for the consideration of hospitalized burn patients for the influenza vaccine. We suggest avoidance of vaccine administration in the acute burn phase. Further prospective clinical trials would be required to validate these findings.

Seasonal influenza vaccination in Kenya: an economic evaluation using dynamic transmission modelling

BACKGROUND

There is substantial burden of seasonal influenza in Kenya, which led the government to consider introducing a national influenza vaccination programme. Given the cost implications of a nationwide programme, local economic evaluation data are needed to inform policy on the design and benefits of influenza vaccination. We set out to estimate the cost-effectiveness of seasonal influenza vaccination in Kenya.

METHODS

We fitted an age-stratified dynamic transmission model to active surveillance data from patients with influenza from 2010 to 2018. Using a societal perspective, we developed a decision tree cost-effectiveness model and estimated the incremental cost-effectiveness ratio (ICER) per disability-adjusted life year (DALY) averted for three vaccine target groups: children 6-23 months (strategy I), 2-5 years (strategy II) and 6-14 years (strategy III) with either the Southern Hemisphere influenza vaccine (Strategy A) or Northern Hemisphere vaccine (Strategy B) or both (Strategy C: twice yearly vaccination campaigns, or Strategy D: year-round vaccination campaigns). We assessed cost-effectiveness by calculating incremental net monetary benefits (INMB) using a willingness-to-pay (WTP) threshold of 1-51% of the annual gross domestic product per capita ($17-$872).

RESULTS

The mean number of infections across all ages was 2-15 million per year. When vaccination was well timed to influenza activity, the annual mean ICER per DALY averted for vaccinating children 6-23 months ranged between $749 and $1385 for strategy IA, $442 and $1877 for strategy IB, $678 and $4106 for strategy IC and $1147 and $7933 for strategy ID. For children 2-5 years, it ranged between $945 and $1573 for strategy IIA, $563 and $1869 for strategy IIB, $662 and $4085 for strategy IIC, and $1169 and $7897 for strategy IID. For children 6-14 years, it ranged between $923 and $3116 for strategy IIIA, $1005 and $2223 for strategy IIIB, $883 and $4727 for strategy IIIC and $1467 and $6813 for strategy IIID. Overall, no vaccination strategy was cost-effective at the minimum ($17) and median ($445) WTP thresholds. Vaccinating children 6-23 months once a year had the highest mean INMB value at $872 (WTP threshold upper limit); however, this strategy had very low probability of the highest net benefit.

CONCLUSION

Vaccinating children 6-23 months once a year was the most favourable vaccination option; however, the strategy is unlikely to be cost-effective given the current WTP thresholds.

Assessment of indirect protection from maternal influenza immunization among non-vaccinated household family members in a randomized controlled trial in Sarlahi, Nepal

•

Acute respiratory infections, including influenza, are common among household member in Nepal.

•

Antenatal influenza vaccination does not confer indirect protection to household members.

•

Challenges include low vaccine efficacy and limited population coverage.

Influenza is a significant cause of morbidity and mortality worldwide, and the World Health Organization highly recommends maternal vaccination during pregnancy. The indirect effect of maternal vaccination on other close contacts other than newborns is unknown. To evaluate this, we conducted a nested substudy between 2011 and 2012 of influenza and acute respiratory illness (ARI) among household members of pregnant women enrolled in a randomized placebo-controlled trial of antenatal influenza vaccination in the rural district of Sarlahi, Nepal. Women were assigned to receive influenza vaccination or placebo during pregnancy and then they and their household members were followed up to 6 months postpartum with weekly symptom surveillance and nasal swab collection. Swabs were tested by RT-PCR for influenza. Rates of laboratory-confirmed influenza and of ARI were compared between vaccine and placebo groups using generalized estimating equations with a Poisson link function. Overall, 1752 individuals in 520 households were eligible for inclusion. There were 82 laboratory-confirmed influenza illness episodes, for a rate of 7.0 per 100 person-years overall. Of the influenza strains able to be typed, 29 were influenza A, 40 were influenza B, and 6 were coinfections with influenza A and B. The rate did not differ significantly whether the household was in the vaccine or placebo group (rate ratio (RR) 1.37, 95% confidence interval (CI) 0.83–2.26). The rate of ARI was 28.5 per 100 person-years overall and did not differ by household group (RR 0.99, 95% CI 0.72–1.36). Influenza vaccination of pregnant women did not provide indirect protection of unvaccinated household members.

Assessing direct and indirect effects of pediatric influenza vaccination in Germany by individual-based simulations

Children have a high burden of influenza and play a central role in spreading influenza. Routinely vaccinating children against influenza may, thus, not only reduce their disease burden, but also that of the general population, including the elderly who frequently suffer severe complications. Using the published individual-based tool 4Flu, we simulated how pediatric vaccination would change infection incidence in Germany. Transmission of four influenza strains was simulated in 100,000 individuals with German demography and contact structure. After initialization with the recorded trivalent influenza vaccination coverage for 20 years (1997-2016), all vaccinations were switched to quadrivalent influenza vaccine (QIV). Scenarios where vaccination coverage of children (0.5-17-year-old) was increased from the current value (4.3%) to a maximum of 10-60% were compared to baseline with unchanged coverage, averaging results of 1,000 pairs of simulations over a 20-year evaluation period (2017-2036). Pediatric vaccination coverage of 10-60% annually prevented 218-1,732 (6.3-50.5%) infections in children, 204-1,961 (2.9-28.2%) in young adults and 95-868 (3.1-28.9%) in the elderly in a population of 100,000 inhabitants; overall, 34.1% of infections in the total population (3.7 million infections per year in Germany) can be prevented if 60% of all children are vaccinated annually. 4.4-4.6 vaccinations were needed to prevent one infection among children; 1.7-1.8 were needed to prevent one in the population. Enhanced pediatric vaccination prevents many infections in children and even more in young adults and the elderly.

Effects of Influenza Vaccination in the United States During the 2017-2018 Influenza Season

BACKGROUND

The severity of the 2017-2018 influenza season in the United States was high, with influenza A(H3N2) viruses predominating. Here, we report influenza vaccine effectiveness (VE) and estimate the number of vaccine-prevented influenza-associated illnesses, medical visits, hospitalizations, and deaths for the 2017-2018 influenza season.

METHODS

We used national age-specific estimates of 2017-2018 influenza vaccine coverage and disease burden. We estimated VE against medically attended reverse-transcription polymerase chain reaction-confirmed influenza virus infection in the ambulatory setting using a test-negative design. We used a compartmental model to estimate numbers of influenza-associated outcomes prevented by vaccination.

RESULTS

The VE against outpatient, medically attended, laboratory-confirmed influenza was 38% (95% confidence interval [CI], 31%-43%), including 22% (95% CI, 12%-31%) against influenza A(H3N2), 62% (95% CI, 50%-71%) against influenza A(H1N1)pdm09, and 50% (95% CI, 41%-57%) against influenza B. We estimated that influenza vaccination prevented 7.1 million (95% CrI, 5.4 million-9.3 million) illnesses, 3.7 million (95% CrI, 2.8 million-4.9 million) medical visits, 109 000 (95% CrI, 39 000-231 000) hospitalizations, and 8000 (95% credible interval [CrI], 1100-21 000) deaths. Vaccination prevented 10% of expected hospitalizations overall and 41% among young children (6 months-4 years).

CONCLUSIONS

Despite 38% VE, influenza vaccination reduced a substantial burden of influenza-associated illness, medical visits, hospitalizations, and deaths in the United States during the 2017-2018 season. Our results demonstrate the benefit of current influenza vaccination and the need for improved vaccines.

Exploring indirect protection associated with influenza immunization - A systematic review of the literature

BACKGROUND

Influenza causes significant annual morbidity and mortality, particularly in older adults, for whom influenza vaccine effectiveness (VE) is also lower. Immunizing one group (e.g., children) against influenza may indirectly protect another group (e.g., older adults) against influenza and its complications.

METHODS

We updated previous systematic reviews on indirect protection against influenza by searching MEDLINE and EMBASE for relevant human studies published until January 4, 2017. We abstracted and critically appraised English language publications that reported or provided information to calculate indirect VE against influenza, as a percentage, in non-institutional settings. We developed a term called 'estimated actual protection' to explore the relationship between indirect protection and the product of direct VE and relative vaccine coverage. We calculated estimated actual protection for a subset of studies that reported coverage and indirect VE for: laboratory-confirmed influenza; outpatient care for respiratory illness; influenza-associated emergency visits; or influenza-associated hospitalizations. We ran linear mixed models to compare estimated actual protection against indirect VE for the four outcomes, and graphed the data.

RESULTS

Of 2320 unique records identified, we abstracted and appraised 26 articles describing 24 studies. The majority of included studies reported at least one outcome suggesting that immunizing one group reduced influenza-related outcomes in another group. Critical appraisal of the abstracted studies identified recurring methodological weaknesses, such as lack of laboratory-confirmed influenza. Our exploratory analyses of 18 studies indicated a positive but not statistically significant relationship between estimated actual protection and indirect protection for each of the four outcomes.

CONCLUSIONS

Our systematic review and exploratory analyses suggest influenza immunization provides some level of indirect protection. However, our critical appraisal highlights the need for a standardized and consistently applied approach to measuring indirect protection against influenza to fill existing knowledge gaps. Additionally, the concept of estimated actual protection requires validation.

Effectiveness of seasonal inactivated influenza vaccination in Japanese schoolchildren: an epidemiologic study at the community level

Influenza vaccination is the most effective method for preventing influenza virus infection. The incidence of influenza is higher in schoolchildren than other age groups. This study evaluated the effectiveness of seasonal inactivated influenza vaccination (IIV) in a community population of schoolchildren during two seasons. This study was a cross-sectional survey of public schoolchildren based on data collected in the 2012/2013 and 2014/2015 seasons. The questionnaire was distributed to all public schoolchildren of target grade in a survey area, and 7945 respondents were included in the analysis. The vaccination status and influenza onset were defined based on the self-reported questionnaire by parents or guardians. Generalized linear mixed models were used to adjust clustering within schools and individual covariates and calculate odds ratios (ORs) and 95% confidence intervals (CIs) for associations between vaccination status and influenza onset. The influenza incidence was higher in the 2015 than the 2013 survey (25% versus 17%), although the vaccination rates were comparable between the two seasons. Receiving one- or two-dose vaccination was more protective against influenza than non-vaccination in both the 2013 (OR, 0.77; 95%CI, 0.65-0.92) and 2015 (OR, 0.88; 95%CI, 0.75-1.02) surveys. Full vaccination was also more protective in both the 2013 (OR, 0.75; 95%CI, 0.62-0.89) and 2015 (OR, 0.86; 95%CI, 0.74-1.00) surveys. Seasonal IIV was protective against influenza for Japanese schoolchildren in a community-based real-world setting. The difference in clinical effectiveness of IIV between the two seasons was likely due to the antigenic mismatch between the circulating and vaccine strains.

Reduction of influenza A(H3N2)-associated symptoms by influenza vaccination in school aged-children during the 2014-2015 winter season dominated by mismatched H3N2 viruses

BACKGROUND

Little is known about the vaccine effectiveness (VE) in attenuating the influenza-associated symptoms in children during the 2014-2015 influenza season in Beijing, China, in which there was a mismatch between the vaccine and circulating strain.

METHODS

This study included 210 laboratory-confirmed influenza cases among children, who were enrolled in 2014, from November 1 to December 31. Standard demographic information and clinical symptoms were recorded. Influenza vaccination was confirmed via a vaccination registry. Univariate and multivariate analyses were used to estimate the odds of presenting with clinical symptoms among vaccinated and unvaccinated groups, adjusting for sex, age, area, BMI level, and chronic conditions.

RESULTS

Among the 210 laboratory-confirmed influenza cases, 170 (81.0%) presented with fever ≥38°C. The other most common symptoms were cough (78.1%), sore throat (46.7%), nasal congestion/rhinorrhea (38.6%), headache (34.8%), fatigue (24.8%) and myalgia/arthralgia (16.2%). Approximately 9.0% (19/210) exhibited nausea/vomiting, and 2.4% (5/210) exhibited diarrhea/abdominal pain. Respiratory complications occurred in 5.7% (12/210) of the confirmed influenza cases. In 210 laboratory-confirmed cases, univariate and multivariate conducted after adjusted for the aforementioned characteristics suggested that the odds of fever ≥ 38°C were significantly reduced in vaccinated children (odds ratio [OR]: 0.42, 95% CI: 0.19-0.93; P = 0.033).

CONCLUSIONS

Influenza vaccination may reduce the clinical symptoms of laboratory-confirmed influenza cases potentially even in the mismatching season.

Indirect protection from vaccinating children against influenza in households

Vaccination is an important intervention to prevent influenza virus infection, but indirect protection of household members of vaccinees is not fully known. Here, we analyze a cluster household randomized controlled trial, with one child in each household randomized to receive influenza vaccine or placebo, for an influenza B epidemic in Hong Kong. We apply statistical models to estimate household transmission dynamics and quantify the direct and indirect protection of vaccination. Direct vaccine efficacy was 71%. The infection probability of unvaccinated household members in vaccinated households was only 5% lower than in control households, because only 10% of infections are attributed to household transmission. Even when that proportion rises to 30% and all children are vaccinated, we predict that the infection probability for unvaccinated household members would only be reduced by 20%. This suggests that benefits of individual vaccination remain important even when other household members are vaccinated.

Relevance of indirect protection of household members of vaccinees is unclear. Here, Tsang et al. quantify the direct and indirect protection of vaccination in a randomized controlled trial and show that benefits of individual vaccination remain important even when other household members are vaccinated.

Association of influenza outbreaks with advanced pediatric medical support

Retrospective data evaluated increases in advanced medical support for children with medically attended acute respiratory illness (MAARI) during influenza outbreak periods (IOP). Advanced support included hospitalisation, intensive care unit admission, or mechanical ventilation, for children aged 0-17 years hospitalised in Maryland's 50 acute-care hospitals over 12 influenza seasons. Weekly numbers of positive influenza tests in the Maryland area defined IOP for each season as the fewest consecutive weeks, including the peak week containing at least 85% of positive tests with a 2-week buffer on either side of the IOP. Peak IOP (PIOP) was defined as four consecutive weeks containing the peak week with the most number of positive influenza tests. Off-PIOP was defined as the 'shoulder' weeks during each IOP. Non-influenza season (NIS) was the remaining weeks of that study season. Rate ratios of mean daily MAARI-related admissions resulting in advanced medical support outcomes during PIOP or Off-PIOP were compared with the NIS and were significantly elevated for all 12 study seasons combined. The results suggest that influenza outbreaks are associated with increased advanced medical support utilisation by children with MAARI. We feel that this data may help preparedness for severe influenza epidemics or pandemic.

The Hurdles From Bench to Bedside in the Realization and Implementation of a Universal Influenza Vaccine

Influenza viruses circulate worldwide causing annual epidemics that have a substantial impact on public health. This is despite vaccines being in use for over 70 years and currently being administered to around 500 million people each year. Improvements in vaccine design are needed to increase the strength, breadth, and duration of immunity against diverse strains that circulate during regular epidemics, occasional pandemics, and from animal reservoirs. Universal vaccine strategies that target more conserved regions of the virus, such as the hemagglutinin (HA)-stalk, or recruit other cellular responses, such as T cells and NK cells, have the potential to provide broader immunity. Many pre-pandemic vaccines in clinical development do not utilize new vaccine platforms but use "tried and true" recombinant HA protein or inactivated virus strategies despite substantial leaps in fundamental research on universal vaccines. Significant hurdles exist for universal vaccine development from bench to bedside, so that promising preclinical data is not yet translating to human clinical trials. Few studies have assessed immune correlates derived from asymptomatic influenza virus infections, due to the scale of a study required to identity these cases. The realization and implementation of a universal influenza vaccine requires identification and standardization of set points of protective immune correlates, and consideration of dosage schedule to maximize vaccine uptake.

Spillover effects on health outcomes in low- and middle-income countries: a systematic review

Background

Many interventions delivered to improve health may benefit not only direct recipients but also people in close physical or social proximity. Our objective was to review all published literature about the spillover effects of interventions on health outcomes in low-middle income countries and to identify methods used in estimating these effects.

Methods

We searched 19 electronic databases for articles published before 2014 and hand-searched titles from 2010 to 2013 in five relevant journals. We adapted the Cochrane Collaboration’s quality grading tool for spillover estimation and rated the quality of evidence.

Results

A total of 54 studies met inclusion criteria. We found a wide range of terminology used to describe spillovers, a lack of standardization among spillover methods and poor reporting of spillovers in many studies. We identified three primary mechanisms of spillovers: reduced disease transmission, social proximity and substitution of resources within households. We found the strongest evidence for spillovers through reduced disease transmission, particularly vaccines and mass drug administration. In general, the proportion of a population receiving an intervention was associated with improved health. Most studies were of moderate or low quality. We found evidence of publication bias for certain spillover estimates but not for total or direct effects. To facilitate improved reporting and standardization in future studies, we developed a reporting checklist adapted from the CONSORT framework specific to reporting spillover effects.

Conclusions

We found the strongest evidence for spillovers from vaccines and mass drug administration to control infectious disease. There was little high quality evidence of spillovers for other interventions.

Generalized herd effects and vaccine evaluation: impact of live influenza vaccine on off-target bacterial colonisation

Interactions between pathogens and commensal microbes are major contributors to health and disease. Infectious diseases however are most often considered independent, viewed within a one-host one-pathogen paradigm and, by extension, the interventions used to treat and prevent them are measured and evaluated within this same paradigm. Vaccines, especially live vaccines, by stimulating immune responses or directly interacting with other microbes can alter the environment in which they act, with effects that span across pathogen species. Live attenuated infl uenza vaccines for example, while safe, increase upper respiratory tract bacterial carriage density of important human commensal pathogens like Streptococcus pneumoniae and Staphylococcus aureus. Further, by altering the ecological niche and dynamics of phylogenetically distinct microbes within the host, vaccines may unintentionally affect transmission of non-vaccine targeted pathogens. Thus, vaccine effects may span across species and across scales, from the individual to the population level. In keeping with traditional vaccine herd-effects that indirectly protect even unvaccinated individuals by reducing population prevalence of vaccine-targeted pathogens, we call these cross-species cross-scale effects "generalized herd-effects". As opposed to traditional herd-effects, "generalized" relaxes the assumption that the effect occurs at the level of the vaccine-target pathogen and "herd effect" implies, as usual, that the effects indirectly impact the population at large, including unvaccinated bystanders. Unlike traditional herd-effects that decrease population prevalence of the vaccine-target, generalized herd-effects may decrease or increase prevalence and disease by the off-target pathogen. LAIV, for example, by increasing pneumococcal density in the upper respiratory tract of vaccine recipients, especially children, may increase pneumococcal transmission and prevalence, leading to excess pneumococcal invasive disease in the population, especially among the elderly and others most susceptible to pneumococcal disease. However, these effects may also be beneficial, for example the large reductions in all-cause mortality noted following measles vaccines. Here we discuss evidence for these novel vaccine effects and suggest that vaccine monitoring and evaluation programs should consider generalized herd effects to appreciate the full impacts of vaccines, beneficial or detrimental, across species and scales that are inevitably hiding in plain sight, affecting human health and disease.

Impact of increased influenza vaccination in 2-3-year-old children on disease burden within the general population: A Bayesian model-based approach

Introduction

During the 2013–2014 influenza season, Public Health England extended routine influenza vaccination to all 2- and 3-year-old children in England. To estimate the impact of this change in policy on influenza-related morbidity and mortality, we developed a disease transmission and surveillance model informed by real-world data.

Methods

We combined real-world and literature data sources to construct a model of influenza transmission and surveillance in England. Data were obtained for four influenza seasons, starting with the 2010–2011 season. Bayesian inference was used to estimate model parameters on a season-by-season basis to assess the impact of targeting 2- and 3-year-old children for influenza vaccination. This provided the basis for the construction of counterfactual scenarios comparing vaccination rates of ~2% and ~35% in the 2- and 3- year-old population to estimate reductions in general practitioner (GP) influenza-like-illness (ILI) consultations, respiratory hospitalizations and deaths in the overall population.

Results

Our model was able to replicate the main patterns of influenza across the four seasons as observed through laboratory surveillance data. Targeting 2- and 3-year-old children for influenza vaccination resulted in reductions in the general population of between 6.2–9.9% in influenza-attributable GP ILI consultations, 6.1–10.7% in influenza-attributable respiratory hospitalizations, and 5.7–9.4% in influenza-attributable deaths. The decrease in influenza-attributable ILI consultations represents a reduction of between 4.5% and 7.3% across all ILI consultations. The reduction in influenza-attributable respiratory hospitalizations represents a reduction of between 1.2% and 2.3% across all respiratory hospitalizations. Reductions in influenza-attributable respiratory deaths represent a reduction of between 0.9% and 2.4% in overall respiratory deaths.

Conclusion

This study has provided evidence that extending routine influenza vaccination to all healthy children aged 2 and 3 years old leads to benefits in terms of reduced utilization of healthcare resources and fewer respiratory health outcomes and deaths.

Influenza vaccination in preventing outbreaks in schools: A long-term ecological overview

Influenza vaccination is the most effective way to reduce the incidence of influenza infections. However, the role of influenza vaccination, such as school-based influenza vaccination, in preventing the influenza outbreaks in schools remains unclear now. In this study, a total of 286 school febrile outbreaks involving 6863 cases in the Beijing area from September 1, 2006 to March 31, 2017 were analyzed. We also tested 294 circulating strains isolated in Beijing during the same period and compared with that of vaccine strains identified every influenza season. The virological match/mismatch between vaccine strains and circulating strains, and the coverage of vaccination in schools were analyzed against outbreaks during the 11 years. It showed that over 80% school febrile outbreaks were caused by influenza A/B virus, the most frequent being A(H3N2) virus (53.25%), followed by A(H1N1)pdm09 virus (25.11%) and B virus (21.64%). More importantly, low vaccine coverage (in 2006-2007 influenza season) and vaccine mismatch (in 2014-2015 and 2015-2016 influenza season) were associated with an increased number of influenza school outbreaks. High vaccination coverage with a matched vaccine can significantly reduce influenza outbreaks in schools (OR: 0.111, p < .001). We have shown the effectiveness of school-based influenza vaccination in preventing outbreaks using trivalent inactivated influenza vaccine in schools. Thus the school-based vaccine policy should be paid more attention in China and other countries worldwide.

Influenza vaccine use to protect healthy children: A debated topic

At the beginning of this century, a number of studies suggested that in healthy children, particularly those <2years of age, influenza could have a serious and complicated course, as it frequently led to hospitalization and sometimes, albeit rarely, to death. Moreover, pre-schoolers and school-age children were found to be among the most important causes of influenza transmission to the community, as they shed the virus for a longer time than adults and had frequent contact with greater numbers of individuals through day-care and school. These findings led a number of health authorities to modify the official recommendations regarding the use of influenza vaccine in healthy children. Several factors seem to indicate that vaccination against influenza in healthy children of any age and in pregnant women could be effective in preventing the disease in the entire paediatric population and in providing herd immunity in adults and old people as well. The direct advantages of the vaccine seem greater in younger subjects, particularly those <2-3years of age. Vaccination of older children is considered effective by most experts, but high vaccination coverage of these subjects has been difficult to attain. Similar difficulties have been identified for the vaccination of pregnant women. These challenges can be overcome, at least in part, by appropriate information and accurate evaluations of available data. In addition, further studies specifically designed to clarify unresolved problems regarding vaccine use in paediatric and pregnant populations are needed to convince reluctant health authorities. More effective vaccines for younger children as well as improved availability of data regarding the optimal time period for vaccine administration in pregnant women appear relevant in this regard.

Translation of the UK Pediatric Influenza Vaccination Programme in Primary Schools to 13 European Countries Using a Dynamic Transmission Model

Objectives: To simulate the impact of a pediatric influenza vaccination programme using quadrivalent live attenuated influenza vaccine (QLAIV) in Europe by applying coverage rates achieved in the United Kingdom during the 2014-2015 season and to compare the model outcomes to the UK results. Methods: We used a deterministic, age-structured, dynamic transmission model adapted to the demography, contact patterns and influenza incidence of 13 European countries, with a 10-year horizon. The reference strategy was the unchanged country-specific coverage rate, using quadrivalent inactivated vaccine (assumed efficacy against infection from 45% in 1-year-old children to 60% in healthy adults). In the evaluated strategy, 56.8% of 5-10-year-old children were additionally vaccinated with QLAIV (assumed efficacy 80%), as was the case in 2014-2015 in the United Kingdom's primary school pilot areas. Symptomatic influenza cases and associated medical resources (primary care consultations [PCC], hospitalization, intensive care unit [ICU] admissions) were calculated. The evaluated versus reference strategies were compared using odds ratios (ORs) for PCC in the target (aged 5-10-years) and non-target adult (aged >17 years) populations as well as number needed to vaccinate (NNV) with QLAIV to avert one PCC, hospitalization or ICU admission. Model outcomes, averaged over 10 seasons, were compared with published real-life data from the United Kingdom for the 2014-2015 season. Results: Over 13 countries and 10 years, the evaluated strategy prevented 32.8 million of symptomatic influenza cases (172.3 vs 205.2 million). The resulting range of ORs for PCC was 0.18-0.48 among children aged 5-10-years, and the published OR in the United Kingdom was 0.06 (95% confidence interval [0.01; 0.62]). In adults, the range of ORs for PCC was 0.60-0.91 (UK OR=0.41 [0.19; 0.86]). NNV ranges were 6-19 per averted PCC (UK NNV=16), 530-1524 per averted hospitalization (UK NNV=317) and 5298-15 241 per averted ICU admission (UK NNV=2205). Conclusions: Across a range of European countries, our model shows the beneficial direct and indirect impact of a paediatric vaccination programme using QLAIV in primary school-aged children, consistent with what was observed during a single season in the United Kingdom. Recommendations for the implementation of pediatric vaccination programmes are, therefore, supported in Europe.

Urgent challenges in implementing live attenuated influenza vaccine

Conflicting reports have emerged about the effectiveness of the live attenuated influenza vaccine. The live attenuated influenza vaccine appears to protect particularly poorly against currently circulating H1N1 viruses that are derived from the 2009 pandemic H1N1 viruses. During the 2015-16 influenza season, when pandemic H1N1 was the predominant virus, studies from the USA reported a complete lack of effectiveness of the live vaccine in children. This finding led to a crucial decision in the USA to recommend that the live vaccine not be used in 2016-17 and to switch to the inactivated influenza vaccine. Other countries, including the UK, Canada, and Finland, however, have continued to recommend the use of the live vaccine. This policy divergence and uncertainty has far reaching implications for the entire global community, given the importance of the production capabilities of the live attenuated influenza vaccine for pandemic preparedness. In this Personal View, we discuss possible explanations for the observed reduced effectiveness of the live attenuated influenza vaccine and highlight the underpinning scientific questions. Further research to understand the reasons for these observations is essential to enable informed public health policy and commercial decisions about vaccine production and development in coming years.

Estimating Direct and Indirect Protective Effect of Influenza Vaccination in the United States

With influenza vaccination rates in the United States recently exceeding 45% of the population, it is important to understand the impact that vaccination is having on influenza transmission. In this study, we used a Bayesian modeling approach, combined with a simple dynamical model of influenza transmission, to estimate this impact. The combined framework synthesized evidence from a range of data sources relating to influenza transmission and vaccination in the United States. We found that, for seasonal epidemics, the number of infections averted ranged from 9.6 million in the 2006-2007 season (95% credible interval (CI): 8.7, 10.9) to 37.2 million (95% CI: 34.1, 39.6) in the 2012-2013 season. Expressed in relative terms, the proportion averted ranged from 20.8% (95% CI: 16.8, 24.3) of potential infections in the 2011-2012 season to 47.5% (95% CI: 43.7, 50.8) in the 2008-2009 season. The percentage averted was only 1.04% (95% CI: 0.15, 3.2) for the 2009 H1N1 pandemic, owing to the late timing of the vaccination program in relation to the pandemic in the Northern hemisphere. In the future, further vaccination coverage, as well as improved influenza vaccines (especially those offering better protection in the elderly), could have an even stronger effect on annual influenza epidemics.

Is the onset of influenza in the community age-related?

We studied the spread of influenza in the community between 1993 and 2009 using primary-care surveillance data to investigate if the onset of influenza was age-related. Virus detections [A(H3N2), B, A(H1N1)] and clinical incidence of influenza-like illness (ILI) in 12·3 million person-years in the long-running Royal College of General Practitioners-linked clinical-virological surveillance programme in England & Wales were examined. The number of days between symptom onset and the all-age peak ILI incidence were compared by age group for each influenza type/subtype. We found that virus detection and ILI incidence increase, peak and decrease were in unison. The mean interval between symptom onset to peak ILI incidence in virus detections (all ages) was: A(H3N2) 20·5 [95% confidence interval (CI) 19·7-21·6] days; B, 18·8 (95% CI 15·8·0-21·7) days; and A(H1N1) 17·0 (95% CI 15·6-18·4) days. Differences by age group were examined using the Kruskal-Wallis test. For A(H3N2) and A(H1N1) viruses the interval was similar in each age group. For influenza B there were highly significant differences by age group (P = 0·0001). Clinical incidence rates of ILI reported in the 8 weeks preceding the period of influenza virus activity were used to estimate a baseline incidence and threshold value (upper 95% CI of estimate) which was used as a marker of epidemic progress. Differences between the age groups in the week in which the threshold was reached were small and not localized to any age group. In conclusion we found no evidence to suggest that influenza A(H3N2) and A(H1N1) occurs in the community in one age group before another. For influenza B, virus detection was earlier in children aged 5-14 years than in persons aged ⩾25 years.

Direct and indirect effects of influenza vaccination

BACKGROUND

After vaccination, vaccinees acquire some protection against infection and/or disease. Vaccination, therefore, reduces the number of infections in the population. Due to this herd protection, not everybody needs to be vaccinated to prevent infections from spreading.

METHODS

We quantify direct and indirect effects of influenza vaccination examining the standard Susceptible-Infected-Recovered (SIR) and Susceptible-Infected-Recovered-Susceptible (SIRS) model as well as simulation results of a sophisticated simulation tool which allows for seasonal transmission of four influenza strains in a population with realistic demography and age-dependent contact patterns.

RESULTS

As shown analytically for the simple SIR and SIRS transmission models, indirect vaccination effects are bigger than direct ones if the effective reproduction number of disease transmission is close to the critical value of 1. Simulation results for 20-60% vaccination with live influenza vaccine of 2-17 year old children in Germany, averaged over 10 years (2017-26), confirm this result: four to seven times as many influenza cases are prevented among non-vaccinated individuals as among vaccinees. For complications like death due to influenza which occur much more frequently in the unvaccinated elderly than in the vaccination target group of children, indirect benefits can surpass direct ones by a factor of 20 or even more than 30.

CONCLUSIONS

The true effect of vaccination can be much bigger than what would be expected by only looking at vaccination coverage and vaccine efficacy.

Facilitators and barriers of parental attitudes and beliefs toward school-located influenza vaccination in the United States: Systematic review

The study objective was to identify facilitators and barriers of parental attitudes and beliefs toward school-located influenza vaccination in the United States. In 2009, the Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention expanded their recommendations for influenza vaccination to include school-aged children. We conducted a systematic review of studies focused on facilitators and barriers of parental attitudes toward school-located influenza vaccination in the United States from 1990 to 2016. We reviewed 11 articles by use of the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) framework. Facilitators were free/low cost vaccination; having belief in vaccine efficacy, influenza severity, and susceptibility; belief that vaccination is beneficial, important, and a social norm; perception of school setting advantages; trust; and parental presence. Barriers were cost; concerns regarding vaccine safety, efficacy, equipment sterility, and adverse effects; perception of school setting barriers; negative physician advice of contraindications; distrust in vaccines and school-located vaccination programs; and health information privacy concerns. We identified the facilitators and barriers of parental attitudes and beliefs toward school-located influenza vaccination to assist in the evidence-based design and implementation of influenza vaccination programs targeted for children in the United States and to improve influenza vaccination coverage for population-wide health benefits.

Influenza Vaccine Effectiveness in Preventing Influenza Illness Among Children During School-based Outbreaks in the 2014-2015 Season in Beijing, China

BACKGROUND

Little is known about vaccine effectiveness (VE) against nonmedically attended A(H3N2) influenza illness during 2014-2015 when the vaccine component appeared to be a poor match with circulating strains.

METHODS

Forty-three eligible school influenza outbreaks in Beijing, China, from November 1, 2014, to December 31, 2014, were included in this study. The VE of 2014-2015 trivalent inactivated influenza vaccine (IIV3) was assessed in preventing laboratory-confirmed influenza among school-age children through a case-control design, using asymptomatic controls. Influenza vaccination was documented from a vaccination registry. VE was estimated adjusting for age group, sex, rural versus urban area, body mass index, chronic conditions, onset week and schools through a mixed effects logistic regression model.

RESULTS

The average coverage rate of 2014-2015 IIV3 among students across the 43 schools was 47.6%. The fully adjusted VE of 2014-2015 IIV3 against laboratory-confirmed influenza was 38% [95% confidence interval (CI): 12%-57%]. Receipt of previous season's (2013-2014) IIV3 significantly modified VE of the 2014-2015 IIV3; children who received both 2013-2014 and 2014-2015 vaccinations had VE of 29% (95% CI: -8% to 53%), whereas VE for children who received 2014-2015 IIV3 only was 54% (95% CI: 8%-77%).

CONCLUSIONS

VE for 2014-2015 IIV3 against A(H3N2) illness identified in schools was modest. Children who did not receive the prior season's vaccine with a homologous A(H3N2) component may have enjoyed greater protection than repeated vaccinees.

Impact of vaccine herd-protection effects in cost-effectiveness analyses of childhood vaccinations. A quantitative comparative analysis

BACKGROUND

Inclusion of vaccine herd-protection effects in cost-effectiveness analyses (CEAs) can impact the CEAs-conclusions. However, empirical epidemiologic data on the size of herd-protection effects from original studies are limited.

METHODS

We performed a quantitative comparative analysis of the impact of herd-protection effects in CEAs for four childhood vaccinations (pneumococcal, meningococcal, rotavirus and influenza). We considered CEAs reporting incremental-cost-effectiveness-ratios (ICERs) (per quality-adjusted-life-years [QALY] gained; per life-years [LY] gained or per disability-adjusted-life-years [DALY] avoided), both with and without herd protection, while keeping all other model parameters stable. We calculated the size of the ICER-differences without vs with-herd-protection and estimated how often inclusion of herd-protection led to crossing of the cost-effectiveness threshold (of an assumed societal-willingness-to-pay) of $50,000 for more-developed countries or X3GDP/capita (WHO-threshold) for less-developed countries.

RESULTS

We identified 35 CEA studies (20 pneumococcal, 4 meningococcal, 8 rotavirus and 3 influenza vaccines) with 99 ICER-analyses (55 per-QALY, 27 per-LY and 17 per-DALY). The median ICER-absolute differences per QALY, LY and DALY (without minus with herd-protection) were $15,620 (IQR: $877 to $48,376); $54,871 (IQR: $787 to $115,026) and $49 (IQR: $15 to $1,636) respectively. When the target-vaccination strategy was not cost-saving without herd-protection, inclusion of herd-protection always resulted in more favorable results. In CEAs that had ICERs above the cost-effectiveness threshold without herd-protection, inclusion of herd-protection led to crossing of that threshold in 45% of the cases. This impacted only CEAs for more developed countries, as all but one CEAs for less developed countries had ICERs below the WHO-cost-effectiveness threshold even without herd-protection. In several analyses, recommendation for the adoption of the target vaccination strategy depended on the inclusion of the herd protection effect.

CONCLUSIONS

Inclusion of herd-protection effects in CEAs had a substantial impact in the estimated ICERs and made target-vaccination strategies more attractive options in almost half of the cases where ICERs were above the societal-willingness to pay threshold without herd-protection. More empirical epidemiologic data are needed to determine the size of herd-protection effects across diverse settings and also the size of negative vaccine effects, e.g. from serotype substitution.

Herd effect from influenza vaccination in non-healthcare settings: a systematic review of randomised controlled trials and observational studies

Influenza vaccination programmes are assumed to have a herd effect and protect contacts of vaccinated persons from influenza virus infection. We searched MEDLINE, EMBASE, the Cumulative Index to Nursing and Allied Health Literature (CINAHL), Global Health and the Cochrane Central Register of Controlled Trials (CENTRAL) from inception to March 2014 for studies assessing the protective effect of influenza vaccination vs no vaccination on influenza virus infections in contacts. We calculated odds ratios (ORs) and 95% confidence intervals (CIs) using a random-effects model. Of 43,082 screened articles, nine randomised controlled trials (RCTs) and four observational studies were eligible. Among the RCTs, no statistically significant herd effect on the occurrence of influenza in contacts could be found (OR: 0.62; 95% CI: 0.34–1.12). The one RCT conducted in a community setting, however, showed a significant effect (OR: 0.39; 95% CI: 0.26–0.57), as did the observational studies (OR: 0.57; 95% CI: 0.43–0.77). We found only a few studies that quantified the herd effect of vaccination, all studies except one were conducted in children, and the overall evidence was graded as low. The evidence is too limited to conclude in what setting(s) a herd effect may or may not be achieved.

The Impact of Mass School Immunization on School Attendance

The purpose of this study was to assess the impact a free, on-site influenza immunization program could have on attendance in Title 1 schools. Four Title 1 elementary schools participated in the study. Students at 2 schools were offered free FluMist® immunizations on site, and students at 2 control schools were not. Compliance on receiving FluMist® was measured on the percentage of students participating after evaluating for medical exclusions. Documentation on the reason for absences at all 4 schools included self- or parent-reported influenza. Attendance rates for the year also were compared with the previous year for all 4 schools. A comparison was done of total days absent versus total days enrolled between schools receiving FluMist® and schools not receiving the vaccine. Despite the fact that FluMist® is a new vaccine and is not required for children, 57% of those medically eligible to receive it had parental permission and received the vaccine. The 2 schools receiving FluMist® increased their attendance rates from 95.3% and 93.9% to 96.1% and 95.8%. Previously, the comparison schools each had a 94.6% attendance rate; one fell to 94.4% and the other rose very slightly to 94.7%. The differences in self- or parent-reported influenza absences were not significant. However, the difference in days absent between individual vaccinated and nonvaccinated schools was statistically significant.

Herd protection effect of N95 respirators in healthcare workers

Objective

To determine if there was herd protection conferred to unprotected healthcare workers (HCWs) by N95 respirators worn by colleagues.

Methods

Data were analysed from a prospective cluster randomized clinical trial conducted in Beijing, China between 1 December 2008 and 15 January 2009. A minimum compliance level (MCL) of N95 respirators for prevention of clinical respiratory illness (CRI) was set based on various compliance cut-offs. The CRI rates were compared between compliant (≥MCL) and non-compliant (<MCL) N95 wearers by ward, and between non-compliant wearers and control subjects who did not wear masks.

Results

Data were analysed from 949 HCWs who wore N95 respirators and 125 HCWs who did not wear masks. At 50% MCL there were no significant differences in the CRI rates between compliant and non-compliant N95 wearers by ward. In multivariate analysis, the CRI rate in non-compliant HCWs was significantly lower compared with controls (relative risk 0.26; 95% confidence interval 0.08, 0.82).

Conclusion

This study suggests herd protection from use of N95 respirators by colleagues within a hospital ward.

Equity in disease prevention: Vaccines for the older adults - a national workshop, Australia 2014

On the 20th June, 2014 the National Health and Medical Research Council's Centre for Research Excellence in Population Health "Immunisation in under Studied and Special Risk Populations", in collaboration with the Public Health Association of Australia, hosted a workshop "Equity in disease prevention: vaccines for the older adults". The workshop featured international and national speakers on ageing and vaccinology. The workshop was attended by health service providers, stakeholders in immunisation, ageing, primary care, researchers, government and non-government organisations, community representatives, and advocacy groups. The aims of the workshop were to: provide an update on the latest evidence around immunisation for the older adults; address barriers for prevention of infection in the older adults; and identify immunisation needs of these groups and provide recommendations to inform policy. There is a gap in immunisation coverage of funded vaccines between adults and infants. The workshop reviewed provider misconceptions, lack of Randomised Control Trials (RCT) and cost-effectiveness data in the frail elderly, loss of autonomy, value judgements and ageism in health care and the need for an adult vaccination register. Workshop recommendations included recognising the right of elderly people to prevention, the need for promotion in the community and amongst healthcare workers of the high burden of vaccine preventable diseases and the need to achieve high levels of vaccination coverage, in older adults and in health workers involved in their care. Research into new vaccine strategies for older adults which address poor coverage, provider attitudes and immunosenescence is a priority. A well designed national register for tracking vaccinations in older adults is a vital and basic requirement for a successful adult immunisation program. Eliminating financial barriers, by addressing inequities in the mechanisms for funding and subsidising vaccines for the older adults compared to those for children, is important to improve equity of access and vaccination coverage. Vaccination coverage rates should be included in quality indicators of care in residential aged care for older adults. Vaccination is key to healthy ageing, and there is a need to focus on reducing the immunisation gap between adults and children.

Illness absenteeism rates in primary and secondary schools in 2013–2014 in England: was there any impact of vaccinating children of primary-school age against influenza?

A phased introduction of routine influenza vaccination of healthy children was recommended in the UK in 2012, with the aim of protecting both vaccinated children and the wider population through reducing transmission. In the first year of the programme in 2013–2014, 4- to 11-year-olds were targeted in pilot areas across England. This study assesses if this was associated with school absenteeism, an important societal burden of influenza. During the spring 2014 term when influenza predominantly circulated, the proportion of absence sessions due to illness was compared between vaccination pilot and non-pilot areas for primary schools (to measure overall impact) and secondary schools (to measure indirect impact). A linear multilevel regression model was applied, adjusting for clustering within schools and potential school-level confounders, including deprivation, past absenteeism, and ethnicity. Low levels of influenza activity were reported in the community in 2013–2014. Primary schools in pilot areas had a significantly adjusted decrease in illness absenteeism of 0·05% relative to non-pilot schools; equivalent to an average of 4 days per school. In secondary schools, there was no significant indirect impact of being located in a pilot area on illness absenteeism. These insights can be used in conjunction with routine healthcare surveillance data to evaluate the full benefits of such a programme.

Influenza Vaccination of Healthcare Workers and Vaccine Allocation for Healthcare Workers During Vaccine Shortages

Influenza causes substantial morbidity and mortality annually, particularly in high-risk groups such as the elderly, young children, immunosuppressed individuals, and individuals with chronic illnesses. Healthcare-associated transmission of influenza contributes to this burden but is often under-recognized except in the setting of large outbreaks. The Centers for Disease Control and Prevention has recommended annual influenza vaccination for healthcare workers (HCWs) with direct patient contact since 1984 and for all HCWs since 1993. The rationale for these recommendations is to reduce the chance that HCWs serve as vectors for healthcare-associated influenza due to their close contact with high-risk patients and to enhance both HCW and patient safety. Despite these recommendations as well as the effectiveness of interventions designed to increase HCW vaccination rates, the percentage of HCWs vaccinated annually remains unacceptably low. Ironically, at the same time that campaigns have sought to increase HCW vaccination rates, vaccine shortages, such as the shortage during the 2004-2005 influenza season, present challenges regarding allocation of available vaccine supplies to both patients and HCWs. This two-part document outlines the position of the Society for Healthcare Epidemiology of America on influenza vaccination for HCWs and provides guidance for the allocation of influenza vaccine to HCWs during a vaccine shortage based on influenza transmission routes and the essential need for a practical and adaptive strategy for allocation. These recommendations apply to all types of healthcare facilities, including acute care hospitals, long-term-care facilities, and ambulatory care settings.

The role of heterogeneity in contact timing and duration in network models of influenza spread in schools

Influenza poses a significant health threat to children, and schools may play a critical role in community outbreaks. Mathematical outbreak models require assumptions about contact rates and patterns among students, but the level of temporal granularity required to produce reliable results is unclear. We collected objective contact data from students aged 5–14 at an elementary school and middle school in the state of Utah, USA, and paired those data with a novel, data-based model of influenza transmission in schools. Our simulations produced within-school transmission averages consistent with published estimates. We compared simulated outbreaks over the full resolution dynamic network with simulations on networks with averaged representations of contact timing and duration. For both schools, averaging the timing of contacts over one or two school days caused average outbreak sizes to increase by 1–8%. Averaging both contact timing and pairwise contact durations caused average outbreak sizes to increase by 10% at the middle school and 72% at the elementary school. Averaging contact durations separately across within-class and between-class contacts reduced the increase for the elementary school to 5%. Thus, the effect of ignoring details about contact timing and duration in school contact networks on outbreak size modelling can vary across different schools.