Influenza vaccination coverage and effectiveness in young children in Thailand, 2011-2013

Comparing performance of year-round and campaign-mode influenza vaccination strategies among children aged 6-23 months in Kenya: 2019-2021

INTRODUCTION

In 2016, the Kenya National Immunization Technical Advisory Group requested additional programmatic and cost effectiveness data to inform the choice of strategy for a national influenza vaccination program among children aged 6-23 months of age. In response, we conducted an influenza vaccine demonstration project to compare the performance of a year-round versus campaign-mode vaccination strategy. Findings from this demonstration project will help identify essential learning lessons for a national program.

METHODS

We compared two vaccine delivery strategies: (i) a year-round vaccination strategy where influenza vaccines were administered throughout the year at health facilities. This strategy was implemented in Njoro sub-county in Nakuru (November 2019 to October 2021) and Jomvu sub-county in Mombasa (December 2019 to October 2021), (ii) a campaign-mode vaccination strategy where vaccines were available at health facilities over four months. This strategy was implemented in Nakuru North sub-county in Nakuru (June to September 2021) and Likoni sub-county in Mombasa (July to October 2021). We assessed differences in coverage, dropout rates, vaccine wastage, and operational needs.

RESULTS

We observed similar performance between strategies in coverage of the first dose of influenza vaccine (year-round strategy 59.7 %, campaign strategy 63.2 %). The coverage obtained in the year-round sub-counties was similar (Njoro 57.4 %; Jomvu 63.1 %); however, more marked differences between campaign sub-counties were observed (Nakuru North 73.4 %; Likoni 55.2 %). The campaign-mode strategy exceeded the cold chain capacity of participating health facilities, requiring thrice monthly instead of once monthly deliveries, and was associated with a two-fold increase in workload compared to the year-round strategy (168 vaccines administered per day in the campaign strategy versus 83 vaccines administered per day in the year-round strategy).

CONCLUSION

Although both strategies had similar coverage levels, the campaign-mode strategy was associated with considerable operational needs that could significantly impact the immunization program.

Acceptance and accessibility to the early phase COVID-19 vaccination among the healthcare workers and hill tribe population in Thailand

Coronavirus disease 2019 (COVID-19) is a serious emerging disease and an extreme threat to human life. This study aimed to understand the perceptions of hill tribe people living in the border areas of Thailand-Myanmar and health workers regarding the acceptability and accessibility of the COVID-19 vaccine and health workers’ perceptions of the readiness to implement the vaccination program during the early period of national COVID-19 vaccination. A qualitative method was applied to elicit information from key informants who lived in hill tribe villages and the health professionals who served them. The study was conducted in seven hill tribe villages located along the Thailand-Myanmar borders in Mae Fah Luang District, Chiang Rai Province, Thailand. The participants were hill tribe villagers aged 20 years and over; public health care professionals working in village health centers who had primary roles in implementing disease prevention and control measures; and public health care professionals working in districts and provincial public health offices who had primary roles in policy development and implementation. A total of 63 participants (26 men and 37 women) from seven hill tribe villages provided information. Three acceptance choices regarding receiving the COVID-19 vaccine were found among the hill tribes: definite acceptance, likely acceptance, and no preference. Two factors related to obtaining access to the new COVID-19 vaccine were found: Thai citizenship and the level of literacy related to the vaccine. There was no process or protocol in place for implementing the new vaccine among health professionals working at the district, subdistrict, or community levels, but the national expanded immunization program (EPI) system was clearly demonstrated to extend throughout the health service chain in Thailand. During the early period of national COVID-19 vaccine implantation in Thailand, not all members of the hill tribes accepted the vaccine; participant acceptance depended on several factors, including a participant’s previous experience with vaccination, whether he or she required more information before making a decision, etc. While acceptance of the vaccine depended on the individual’s background, not everyone had an equal opportunity to access the vaccine. The new COVID-19 vaccine should be available at the village level, including in hill tribe villages, to reduce the systemic threat to the country.

Cost-effectiveness of seasonal influenza vaccination in pregnant women, healthcare workers and adults >= 60 years of age in Lao People's Democratic Republic

BACKGROUND

Pregnant women, healthcare workers (HW), and adults >= 60 years have shown an increased vulnerability to seasonal influenza virus infections and/or complications. In 2012, the Lao People's Democratic Republic (Lao PDR) initiated a national influenza vaccination program for these target groups. A cost-effectiveness evaluation of this program was undertaken to inform program sustainability.

METHODS

We designed a decision-analytical model and collected influenza-related medical resource utilization and cost data, including indirect costs. Model inputs were obtained from medical record abstraction, interviews of patients and staff at hospitals in the national influenza sentinel surveillance system and/or from literature reviews. We compared the annual disease and economic impact of influenza illnesses in each of the target groups in Lao PDR under scenarios of no vaccination and vaccination, and then estimated the cost-effectiveness of the vaccination program. We performed sensitivity analyses to identify influential variables.

RESULTS

Overall, the vaccination of pregnant women, HWs, and adults >= 60 years could annually save 11,474 doctor visits, 1,961 days of hospitalizations, 43,027 days of work, and 1,416 life-years due to laboratory-confirmed influenza illness. After comparing the total vaccination program costs of 23.4 billion Kip, to the 18.4 billion Kip saved through vaccination, we estimated the vaccination program to incur a net cost of five billion Kip (599,391 USD) annually. The incremental cost per life-year saved (ICER) was 44 million Kip (5,295 USD) and 6.9 million Kip (825 USD) for pregnant women and adults >= 60 years, respectively. However, vaccinating HWs provided societal cost-savings, returning 2.88 Kip for every single Kip invested. Influenza vaccine effectiveness, attack rate and illness duration were the most influential variables to the model.

CONCLUSION

Providing influenza vaccination to HWs in Lao PDR is cost-saving while vaccinating pregnant women and adults >= 60 is cost-effective and highly cost-effective, respectively, per WHO standards.

Etiology and Clinical Characteristics of Severe Pneumonia Among Young Children in Thailand: Pneumonia Etiology Research for Child Health (PERCH) Case-Control Study Findings, 2012-2013

BACKGROUND

Pneumonia remains the leading cause of death among children <5 years of age beyond the neonatal period in Thailand. Using data from the Pneumonia Etiology Research for Child Health (PERCH) Study, we provide a detailed description of pneumonia cases and etiology in Thailand to inform local treatment and prevention strategies in this age group.

METHODS

PERCH, a multi-country case-control study, evaluated the etiology of hospitalized cases of severe and very severe pneumonia among children 1-59 months of age. The Thailand site enrolled children for 24 consecutive months during January 2012-February 2014 with staggered start dates in 2 provinces. Cases were children hospitalized with pre-2013 WHO-defined severe or very severe pneumonia. Community controls were randomly selected from health services registries in each province. Analyses were restricted to HIV-negative cases and controls. We calculated adjusted odds ratios (ORs) and 95% CIs comparing organism prevalence detected by nasopharyngeal/oropharyngeal (NP/OP) polymerase chain reaction between cases and controls. The PERCH Integrated Analysis (PIA) used Bayesian latent variable analysis to estimate pathogen-specific etiologic fractions and 95% credible intervals.

RESULTS

Over 96% of both cases (n = 223) and controls (n = 659) had at least 1 organism detected; multiple organisms were detected in 86% of cases and 88% of controls. Among 98 chest Radiograph positive (CXR+) cases, respiratory syncytial virus (RSV) had the highest NP/OP prevalence (22.9%) and the strongest association with case status (OR 20.5; 95% CI: 10.2, 41.3) and accounted for 34.6% of the total etiologic fraction. Tuberculosis (TB) accounted for 10% (95% CrI: 1.6-26%) of the etiologic fraction among CXR+ cases.

DISCUSSION

More than one-third of hospitalized cases of severe and very severe CXR+ pneumonia among children 1-59 months of age in Thailand were attributable to RSV. TB accounted for 10% of cases, supporting evaluation for TB among children hospitalized with pneumonia in high-burden settings. Similarities in pneumonia etiology in Thailand and other PERCH sites suggest that global control strategies based on PERCH study findings are relevant to Thailand and similar settings.

Knowledge, attitude/perception, and practice related to seasonal influenza vaccination among caregivers of young Thai children: A cross-sectional study

Background

Seasonal influenza vaccination uptake among young children in Thailand is low despite national recommendation for vaccination. We implemented a knowledge, attitude/perception, and practice survey to understand determinants of influenza vaccination in children aged six months to two years.

Methods

Using a cross-sectional design, we interviewed caregivers of 700 children in seven hospitals using a structured questionnaire to collect information on caregivers’ and children’s demographic characteristics, and caregivers’ knowledge of influenza illness and national vaccine recommendation, attitude/perception toward influenza vaccine, and information sources. We verified children’s influenza vaccination status against medical records (vaccinated vs. unvaccinated). Logistic regression was used to examine factors independently associated with children receiving influenza vaccination in the 2018 season using the dataset restricted to only children’s parents. Variables associated with vaccination at p-value ≤0.20 were included in subsequent multivariable logistic models. Significant independent determinants of children’s influenza vaccination and collinearity of covariates were assessed. The final model was constructed using a stepwise backward elimination approach with variables significant at p-value <0.05 retained in the model.

Results

During August 2018-February 2019, 700 children’s caregivers completed the questionnaire; 61 (9%) were caregivers of vaccinated children. Caregivers of the vaccinated children were statistically more likely to have higher education (61% vs. 38%; p-value<0.01) and to know of influenza illness (93% vs. 76%; p-value = 0.03) than those of the unvaccinated group. Factors associated with children receiving influenza vaccination were identifying healthcare providers as a primary source of information about influenza illness for parents (adjusted odds ratio [aOR], 2.8; 95% confidence interval [CI], 1.3–6.0), parents’ strongly agreeing with the national recommendation for influenza vaccination in young children (aOR, 2.9; 95% CI, 1.5–5.9), using health insurance provided by the government or parent’s employer for children’s doctor visits (aOR, 2.6; 95% CI, 1.1–6.6), and the children’s history of receiving influenza vaccination in the 2017 season or earlier (aOR, 3.2; 95% CI, 1.4–7.8).

Conclusion

The majority of caregivers of children in this study had knowledge of influenza illness and influenza vaccine. Caregivers reported various sources of information regarding influenza illness and the vaccine, but healthcare providers remained the most trusted source. Children’s history of influenza vaccination in prior season(s) was the strongest determinant of children being vaccinated for influenza in the current season.

Influenza-Associated Medical Visits Prevented by Influenza Vaccination in Young Children in Thailand, 2012-2014

Despite recommendations, few children aged 6-35 months in Thailand receive seasonal influenza vaccination. Using previously estimated incidence and vaccine effectiveness data from the period 2012-2014, we estimate that up to 121 000 medical visits could be prevented each year with 50% coverage and expanded recommendations to children aged <5 years.

Economic Burden of Influenza in Thailand: A Systematic Review

Thailand has a high incidence and high mortality rates of influenza. This study summarizes the evidence on economic burden or costs of influenza subsequent to the occurrence of influenza illness in the Thai population by specific characteristics such as population demographics, health conditions, healthcare facilities, and/or cost types from published literature. A systematic search was conducted in six electronic databases. All costs were extracted and adjusted to 2018 US dollar value. Out of 581 records, 11 articles (1 with macroeconomic analysis and 10 with microeconomic analyses) were included. Direct medical costs per episode for outpatients and inpatients ranged from US$4.21 to US$212.17 and from US$163.62 to US$4577.83, respectively, across distinct influenza illnesses. The overall burden of influenza was between US$31.1 and US$83.6 million per year and 50-53% of these estimates referred to lost productivity. Costs of screening for an outbreak of influenza at an 8-bed-intensive-care-unit hospital was US$38242.75 per year. Labor-sensitive sectors such as services were the most affected part of the Thai economy. High economic burden tended to occur among children and older adults with co-morbidities and to be related to complications, non-vaccinated status, and severe influenza illness. Strategies involving prevention, limit of transmission, and treatment focusing on aforementioned patients’ factors, containment of hospitalization expenses and quarantine process, and assistance on labor-sensitive economy sectors are likely to reduce the economic burden of influenza. However, a research gap exists regarding knowledge about the economic burden of influenza in Thailand.

Genetic analysis of HA1 domain of influenza A/H3N2 viruses isolated in Kenya during the 2007-2013 seasons reveal significant divergence from WHO-recommended vaccine strains

BACKGROUND

Influenza viruses evolve rapidly and cause regular seasonal epidemics in humans challenging effective vaccination. The virus surface HA glycoprotein is the primary target for the host immune response. Here, we investigated the vaccine efficacy and evolution patterns of human influenza A/H3N2 viruses that circulated in Kenyan in the period before and after the 2009 A/H1N1 pandemic, targeting the HA1 domain.

MATERIALS AND METHODS

A hundred and fifteen HA sequences of Kenyan virus viruses were analyzed relative to the corresponding WHO vaccine reference strains using bioinformatics approaches.

RESULTS

Our analyses revealed varied amino acid substitutions at all the five antigenic sites (A-E) of the HA1 domain, with a majority the changes occurring at sites A and B. The Kenyan A/H3N2 viruses isolated during 2007/2008 seasons belonged to A/Brisbane/10/2007-like viruses lineage, while those circulating in 2009-2012 belonged to the lineage of A/Victoria/361/2011-like viruses. The 2013 viruses clustered in clade 3C.3 of the A/Samara/73/2013-like viruses. The mean evolutionary rate of the A/H3N2 viruses analyzed in the study was at 4.17×10^-3 (95% HPD=3.09×10^-3-5.31×10^-3) nucleotide substitutions per site per year, whereas the TMRCA was estimated at 11.18 (95% HPD=9.00-14.12) years ago from 2013. The prediction of vaccine efficacy revealed modest vaccine efficaciousness during 2008, and 2010 influenza seasons, whilst sub-optimal effectiveness was registered in 2007, 2009, 2012 and 2013. Further, the overall selective pressure acting on the HA1 domain was estimated at 0.56 (ω<1), suggesting that a majority of codon sites in the HA1 epitopes were evolving under purifying selection.

CONCLUSIONS

Generally, our results highlight the genetic plasticity of A/H3N2 viruses and reveal considerable disparity in vaccine efficaciousness against the A/H3N2 viruses that circulated in Kenya, specifically during 2007, 2009, 2012, and 2013 influenza seasons. Our findings underscore the importance and need for consistent surveillance and molecular characterization of influenza viruses, to inform decision making and enhance early of detection of strains with epidemic/pandemic potential as well as benefit in guiding decisions regarding the appropriate annual influenza vaccine formulations.

Global burden of respiratory infections associated with seasonal influenza in children under 5 years in 2018: a systematic review and modelling study

BACKGROUND

Seasonal influenza virus is a common cause of acute lower respiratory infection (ALRI) in young children. In 2008, we estimated that 20 million influenza-virus-associated ALRI and 1 million influenza-virus-associated severe ALRI occurred in children under 5 years globally. Despite this substantial burden, only a few low-income and middle-income countries have adopted routine influenza vaccination policies for children and, where present, these have achieved only low or unknown levels of vaccine uptake. Moreover, the influenza burden might have changed due to the emergence and circulation of influenza A/H1N1pdm09. We aimed to incorporate new data to update estimates of the global number of cases, hospital admissions, and mortality from influenza-virus-associated respiratory infections in children under 5 years in 2018.

METHODS

We estimated the regional and global burden of influenza-associated respiratory infections in children under 5 years from a systematic review of 100 studies published between Jan 1, 1995, and Dec 31, 2018, and a further 57 high-quality unpublished studies. We adapted the Newcastle-Ottawa Scale to assess the risk of bias. We estimated incidence and hospitalisation rates of influenza-virus-associated respiratory infections by severity, case ascertainment, region, and age. We estimated in-hospital deaths from influenza virus ALRI by combining hospital admissions and in-hospital case-fatality ratios of influenza virus ALRI. We estimated the upper bound of influenza virus-associated ALRI deaths based on the number of in-hospital deaths, US paediatric influenza-associated death data, and population-based childhood all-cause pneumonia mortality data in six sites in low-income and lower-middle-income countries.

FINDINGS

In 2018, among children under 5 years globally, there were an estimated 109·5 million influenza virus episodes (uncertainty range [UR] 63·1-190·6), 10·1 million influenza-virus-associated ALRI cases (6·8-15·1); 870 000 influenza-virus-associated ALRI hospital admissions (543 000-1 415 000), 15 300 in-hospital deaths (5800-43 800), and up to 34 800 (13 200-97 200) overall influenza-virus-associated ALRI deaths. Influenza virus accounted for 7% of ALRI cases, 5% of ALRI hospital admissions, and 4% of ALRI deaths in children under 5 years. About 23% of the hospital admissions and 36% of the in-hospital deaths were in infants under 6 months. About 82% of the in-hospital deaths occurred in low-income and lower-middle-income countries.

INTERPRETATION

A large proportion of the influenza-associated burden occurs among young infants and in low-income and lower middle-income countries. Our findings provide new and important evidence for maternal and paediatric influenza immunisation, and should inform future immunisation policy particularly in low-income and middle-income countries.

FUNDING

WHO; Bill & Melinda Gates Foundation.

Immunogenicity and safety of a Trivalent Influenza HA vaccine in Indonesian infants and children

INTRODUCTION

High rate of influenza infection in children made influenza vaccination strongly recommended for all person aged >6 months in Indonesia. Bio Farma Trivalent Influenza HA (Flubio®) vaccine has been used in adolescents and adults, resulted in increased seroconversion, seroprotection rates and geometric mean titer (GMT). However, no data is available regarding its efficacy and safety in children. This study aimed to assess the immunogenicity and safety of Flubio® vaccine in infants and children.

MATERIALS AND METHODS

This was a phase II, open-labeled, clinical trial conducted on healthy children aged 6 month-11 years, vaccinated with 1 or 2 doses of Influenza HA vaccine, with a 28-day interval. Flubio® vaccine composed of A/California/7/2009 (H1N1) pandemic 09, A/Texas/50/2012 (H3N2), and B/Massachusetts/2/2012 strain. This study was held at East Jakarta, Indonesia from May until July 2014. A Total of 405 subjects were included and divided into three groups: A(6-35 months), B(3-8 years), and C(9-11 years). Antibody titer was measured at visit V1 (Day 0), V2 (28 days/+7days after the first dose) and V3 (28 days/+7days after second dose). The seroprotection and seroconversion rates were assessed. Safety was assessed up to 28 days following each dose.

RESULTS

A total of 404 subjects completed the study. After vaccination, all subjects achieved seroprotection and increased seroconversion rates, with post-vaccination antibody titer of ≥1:40 HI for all strains. The GMT also increased significantly. Within 30 min after vaccination, 14.6% and 2% had local and systemic reactions; meanwhile, between 30 min to 72 h after vaccination, 35.1% and 13.6% subjects had local and systemic reactions, respectively. Most reactions were mild. No serious adverse event (SAE) was reported related to vaccine.

CONCLUSION

Flubio® (Influenza HA Trivalent) vaccine is immunogenic and safe for children aged 6 months-11 years.

TRIAL REGISTRATION

The trial is registered at the US National Institutes of Health (ClinicalTrials.gov) #NCT02093260.

Literature review of the epidemiology of influenza B disease in 15 countries in the Asia-Pacific region

Influenza control strategies focus on the use of trivalent influenza vaccines containing two influenza A virus subtypes and one of the two circulating influenza type B lineages (Yamagata or Victoria). Mismatches between the vaccine B lineage and the circulating lineage have been regularly documented in many countries, including those in the Asia‐Pacific region. We conducted a literature review with the aim of understanding the relative circulation of influenza B viruses in Asia‐Pacific countries. PubMed and Western Pacific Region Index Medicus were searched for relevant articles on influenza type B published since 1990 in English language for 15 Asia‐Pacific countries. Gray literature was also accessed. From 4834 articles identified, 121 full‐text articles were analyzed. Influenza was reported as an important cause of morbidity in the Asia‐Pacific region, affecting all age groups. In all 15 countries, influenza B was identified and associated with between 0% and 92% of laboratory‐confirmed influenza cases in any one season/year. Influenza type B appeared to cause more illness in children aged between 1 and 10 years than in other age groups. Epidemiological data for the two circulating influenza type B lineages remain limited in several countries in the Asia‐Pacific, although the co‐circulation of both lineages was seen in countries where strain surveillance data were available. Mismatches between circulating B lineages and vaccine strains were observed in all countries with available data. The data suggest that a shift from trivalent to quadrivalent seasonal influenza vaccines could provide additional benefits by providing broader protection.

Cost-effectiveness of inactivated seasonal influenza vaccination in a cohort of Thai children ≤60 months of age

Background

Vaccination is the best measure to prevent influenza. We conducted a cost-effectiveness evaluation of trivalent inactivated seasonal influenza vaccination, compared to no vaccination, in children ≤60 months of age participating in a prospective cohort study in Bangkok, Thailand.

Methods

A static decision tree model was constructed to simulate the population of children in the cohort. Proportions of children with laboratory-confirmed influenza were derived from children followed weekly. The societal perspective and one-year analytic horizon were used for each influenza season; the model was repeated for three influenza seasons (2012–2014). Direct and indirect costs associated with influenza illness were collected and summed. Cost of the trivalent inactivated seasonal influenza vaccine (IIV3) including promotion, administration, and supervision cost was added for children who were vaccinated. Quality-adjusted life years (QALY), derived from literature, were used to quantify health outcomes. The incremental cost-effectiveness ratio (ICER) was calculated as the difference in the expected total costs between the vaccinated and unvaccinated groups divided by the difference in QALYs for both groups.

Results

Compared to no vaccination, IIV3 vaccination among children ≤60 months in our cohort was not cost-effective in the introductory year (2012 season; 24,450 USD/QALY gained), highly cost-effective in the 2013 season (554 USD/QALY gained), and cost-effective in the 2014 season (16,200 USD/QALY gained).

Conclusion

The cost-effectiveness of IIV3 vaccination among children participating in the cohort study varied by influenza season, with vaccine cost and proportion of high-risk children demonstrating the greatest influence in sensitivity analyses. Vaccinating children against influenza can be economically favorable depending on the maturity of the program, influenza vaccine performance, and target population.

Coverage and factors associated with influenza vaccination among kindergarten children 2-7 years old in a low-income city of north-western China (2014-2016)

Influenza vaccination has been shown to be the most effective preventive measure to reduce influenza virus infection and its related morbidity and mortality. Young children aged 6-59 months are recommended as one of the priority groups for seasonal influenza vaccination in China. Our study was conducted to evaluate the level of influenza vaccination coverage during 2014-15 and 2015-16 influenza seasons among kindergarten children aged 2-7 years in Xining, a low-income city of north-western China, and to explore potential factors for noncompliance associated with influenza vaccination. The coverage rate of influenza vaccination was 12.2% (95 CI: 10.6-14.2%) in 2014-15 and 12.8% (95 CI: 11.1-14.7%) in 2015-16. The low coverage rate was found to be primarily associated with the lack of knowledge about influenza vaccine in children's parents. The most common reason for vaccine declination was the concern about adverse reactions of vaccine. Therefore tailored information should be provided by clinician and public health doctors for targeted groups through effective methods to improve public understanding of vaccination.

Potent protection against H5N1 and H7N9 influenza via childhood hemagglutinin imprinting

Two zoonotic influenza A viruses (IAV) of global concern, H5N1 and H7N9, exhibit unexplained differences in age distribution of human cases. Using data from all known human cases of these viruses, we show that an individual's first IAV infection confers lifelong protection against severe disease from novel hemagglutinin (HA) subtypes in the same phylogenetic group. Statistical modeling shows that protective HA imprinting is the crucial explanatory factor, and it provides 75% protection against severe infection and 80% protection against death for both H5N1 and H7N9. Our results enable us to predict age distributions of severe disease for future pandemics and demonstrate that a novel strain's pandemic potential increases yearly when a group-mismatched HA subtype dominates seasonal influenza circulation. These findings open new frontiers for rational pandemic risk assessment.

Effectiveness of the 2013 and 2014 Southern Hemisphere Influenza Vaccines Against Laboratory-confirmed Influenza in Young Children Using a Test-negative Design, Bangkok, Thailand

BACKGROUND

The Thai Advisory Committee on Immunization Practices recommends annual influenza vaccination for children 6 months through 2 years of age, although older children may be vaccinated on request. We evaluated the effectiveness of the 2013 and 2014 inactivated influenza vaccines to reduce medically attended, laboratory-confirmed influenza illness among Thai children aged 7-60 months.

METHODS

From September 2013-May 2015, children with influenza-like illness were screened with a rapid influenza diagnostic test. Enrolled children had nasal and throat swabs tested for influenza viruses using polymerase chain reaction. Cases and controls were subjects testing positive and negative, respectively, for influenza viruses by polymerase chain reaction. Vaccination status was ascertained from vaccination cards. Vaccine effectiveness (VE) was calculated as 100% × (1 - odds ratio of vaccination among cases vs. controls).

RESULTS

Of the 1377 children enrolled, cases (n = 490) and controls (n = 887) were similar in demographic characteristics. Cases were less likely to receive influenza vaccine than controls in 2013 (6% vs. 14%; P = 0.02), but not in 2014 (6% vs. 7%; P = 0.57). Among cases, 126 (26%) were positive for influenza A(H1N1)pdm09 virus, 239 (49%) for influenza A(H3N2) and 124 (25%) for influenza B. One specimen was positive for both influenza A(H3N2) and B viruses. VE for full vaccination against all viruses was 64% (95% confidence interval: 21% to 84%) in 2013 and 26% (95% confidence interval: -47% to 63%) in 2014.

CONCLUSIONS

Influenza vaccination was low among Thai children in this study, and VE varied by year, highlighting the need for annual monitoring of VE to better understand vaccine program effectiveness.

Epidemiological, Clinical and Virological Characteristics of Influenza B Virus from Patients at the Hospital Tertiary Care Units in Bangkok during 2011-2014

Influenza B virus, which causes acute respiratory infections, has increased in prevalence in recent years. Based on the nucleotide sequence of the hemagglutinin (HA) gene, influenza B virus can be divided into two lineages, Victoria and Yamagata, that co-circulate during the influenza season. However, analysis of the potential association between the clinical and virological characteristic and the lineage of influenza B viruses isolated in Thailand was lacking. To investigate influenza B virus genetically and determine its neuraminidase (NA) inhibitor susceptibility phenotype, a total of 6920 nasopharyngeal-wash samples were collected from patients with influenza-like illness between the years 2011 and 2014 and were screened for influenza B virus by real-time PCR. Of these samples, 3.1% (216/6920) were confirmed to contain influenza B viruses, and 110 of these influenza viruses were randomly selected for nucleotide sequence analysis of the HA and NA genes. Phylogenetic analysis of the HA sequences showed clustering into various clades: Yamagata clade 3 (11/110, 10%), Yamagata clade 2 (71/110, 64.5%), and Victoria clade 1 (28/110, 25.5%). The analysis of clinical characteristic demonstrated that the Victoria lineage was significantly associated with the duration of hospitalization, number of deceased cases, pneumonia, secondary bacterial infection and underlying disease. When combined with phylogenetic analysis of the NA sequences, four samples showed viruses with reassortant sequences between the Victoria and Yamagata lineages. Statistical analysis of the clinical outcomes and demographic data for the reassortant strains did not differ from those of the other strains in circulation. Oseltamivir-resistant influenza B viruses were not detected. Our findings indicated the co-circulation of the Victoria and Yamagata lineages over the past four cold seasons in Bangkok. We also demonstrated differences in the clinical symptoms between these lineages.

Seasonal influenza vaccine policy, use and effectiveness in the tropics and subtropics - a systematic literature review

AIM

The evidence needed for tropical countries to take informed decisions on influenza vaccination is scarce. This article reviews policy, availability, use and effectiveness of seasonal influenza vaccine in tropical and subtropical countries.

METHOD

Global health databases were searched in three thematic areas - policy, availability and protective benefits in the context of human seasonal influenza vaccine in the tropics and subtropics. We excluded studies on monovalent pandemic influenza vaccine, vaccine safety, immunogenicity and uptake, and disease burden.

RESULTS

Seventy-four countries in the tropics and subtropics representing 60% of the world's population did not have a national vaccination policy against seasonal influenza. Thirty-eight countries used the Northern Hemisphere and 21 countries the Southern Hemisphere formulation. Forty-six countries targeted children and 57 targeted the elderly; though, the age cut-offs varied. Influenza vaccine supply increased twofold in recent years. However, coverage remained lower than five per 1000 population. Vaccine protection against laboratory-confirmed influenza in the tropics ranged from 0% to 42% in the elderly, 20-77% in children and 50-59% in healthy adults. Vaccinating pregnant women against seasonal influenza prevented laboratory-confirmed influenza in both mothers (50%) and their infants <6 months (49-63%).

CONCLUSION

Guidelines on vaccine composition, priority risk groups and vaccine availability varied widely. The evidence on vaccine protection was scarce. Countries in the tropics and subtropics need to strengthen and expand their evidence-base required for making informed decisions on influenza vaccine introduction and expansion, and how much benefit to expect.

Assessment of potential public health impact of a quadrivalent inactivated influenza vaccine in Thailand

BACKGROUND

Each year, an influenza B strain representing only one influenza B lineage is included in the trivalent inactivated influenza vaccine (IIV3); a mismatch between the selected lineage and circulating viruses can result in suboptimal vaccine effectiveness. We modeled the added potential public health impact of a quadrivalent inactivated influenza vaccine (IIV4) that includes strains from both influenza B lineages compared to IIV3 on influenza-associated morbidity and mortality in Thailand.

METHODS

Using data on the incidence of influenza-associated hospitalizations and deaths, vaccine effectiveness, and vaccine coverage from the 2007-2012 influenza seasons in Thailand, we estimated rates of influenza-associated outcomes that might be averted using IIV4 instead of IIV3. We then applied these rates to national population estimates to calculate averted illnesses, hospitalizations, and deaths for each season. We assumed that the influenza B lineage included in IIV3 would provide a relative vaccine effectiveness of 75% against the other B lineage.

RESULTS

Compared to use of IIV3, use of IIV4 might have led to an additional reduction ranging from 0·4 to 14·3 influenza-associated illnesses per 100 000 population/year, <0·1 to 0·5 hospitalizations per 100 000/year, and <0·1 to 0·4 deaths per 1000/year. Based on extrapolation to national population estimates, replacement of IIV3 with IIV4 might have averted an additional 267-9784 influenza-associated illnesses, 9-320 hospitalizations, and 0-3 deaths.

CONCLUSION

Compared to use of IIV3, IIV4 has the potential to further reduce the burden of influenza-associated morbidity and mortality in Thailand.

Seasonal influenza vaccine effectiveness against medically attended influenza illness among children aged 6-59 months, October 2011-September 2012: A matched test-negative case-control study in Suzhou, China

BACKGROUND

Seasonal influenza infections among young children in China lead to substantial numbers of hospitalizations and financial burden. This study assessed the seasonal influenza vaccine effectiveness (VE) against laboratory confirmed medically attended influenza illness among children in Suzhou, China, from October 2011-September 2012.

METHODS

We conducted a test-negative case-control study among children aged 6-59 months who sought care at Soochow University Affiliated Children's Hospital (SCH) from October 2011-September 2012. A case was defined as a child with influenza-like illness (ILI) or severe acute respiratory infection (SARI) with an influenza-positive nasopharyngeal swab by rRT-PCR. Controls were selected from children presenting with ILI or SARI without laboratory confirmed influenza. We conducted 1:1 matching by age and admission date. Vaccination status was verified from the citywide immunization system database. VE was calculated with conditional logistic regression: (1-OR)×100%.

RESULT

During the study period, 2634 children aged 6-59 months presented to SCH with ILI (1975) or SARI (659) and were tested for influenza. The vaccination records were available for 69% (1829; ILI: 1354, SARI: 475). Among those, 23% (427) tested positive for influenza, and were included as cases. Among influenza positive cases, the vaccination rates were 3.2% for SARI and 4.5% for ILI. Among controls, the vaccination rates were 13% for SARI, and 11% for ILI. The overall VE against lab-confirmed medically attended influenza virus infection was 67% (95% CI: 41-82). The VE for SARI was 75% (95% CI: 11-93) and for ILI was 64% (95% CI: 31-82).

CONCLUSIONS

The seasonal influenza vaccine was effective against medically attended lab-confirmed influenza infection in children aged 6-59 months in Suzhou, China in the 2011-12 influenza season. Increasing seasonal influenza vaccination among young children in Suzhou may decrease medically attended influenza-associated ILI and SARI cases in this population.

Assessing Antigenic Drift of Seasonal Influenza A(H3N2) and A(H1N1)pdm09 Viruses

Under selective pressure from the host immune system, antigenic epitopes of influenza virus hemagglutinin (HA) have continually evolved to escape antibody recognition, termed antigenic drift. We analyzed the genomes of influenza A(H3N2) and A(H1N1)pdm09 virus strains circulating in Thailand between 2010 and 2014 and assessed how well the yearly vaccine strains recommended for the southern hemisphere matched them. We amplified and sequenced the HA gene of 120 A(H3N2) and 81 A(H1N1)pdm09 influenza virus samples obtained from respiratory specimens and calculated the perfect-match vaccine efficacy using the p_epitope model, which quantitated the antigenic drift in the dominant epitope of HA. Phylogenetic analysis of the A(H3N2) HA1 genes classified most strains into genetic clades 1, 3A, 3B, and 3C. The A(H3N2) strains from the 2013 and 2014 seasons showed very low to moderate vaccine efficacy and demonstrated antigenic drift from epitopes C and A to epitope B. Meanwhile, most A(H1N1)pdm09 strains from the 2012–2014 seasons belonged to genetic clades 6A, 6B, and 6C and displayed the dominant epitope mutations at epitopes B and E. Finally, the vaccine efficacy for A(H1N1)pdm09 (79.6–93.4%) was generally higher than that of A(H3N2). These findings further confirmed the accelerating antigenic drift of the circulating influenza A(H3N2) in recent years.

Influenza vaccine effectiveness in the tropics: moderate protection in a case test-negative analysis of a hospital-based surveillance population in Bangkok between August 2009 and January 2013

Influenza in the tropics occurs year round with peaks that correspond variably to temperate regions. However, data on influenza vaccine effectiveness (VE) in the tropics is sparse. We report on the effectiveness of influenza vaccine to prevent medically attended laboratory confirmed influenza from sentinel surveillance conducted at a Thai military medical facility in Bangkok, Thailand from August 2009 to January 2013. Patients ≥6 months old presenting with influenza-like illness underwent combined nasal/throat swabs which were tested by influenza RT-PCR. A case test-negative study design was used to evaluate VE. Of 2999 samples available for analysis,1059 (35.3%) were PCR-positive (cases) and 1940 (64.6%) were PCR-negative (test-negative controls). Five hundred and seven (16.9%) of these patients reported being vaccinated within the previous 12 months. Periods of high and low influenza activity were defined based on publicly available Thai Ministry of Public Health data. Overall VE adjusted for age and epiweek was found to be 50.1% (95%CI: 35.0, 61.9%). The May to April adjusted VE for year 2010, 2011 and 2012 was 57.7% (95%CI: 33.7, 73.8%), 57.1% (95% CI: 35.2, 68.3%) and 37.6% (95% CI: 3.5, 62.9%).During high influenza activity in years with the same vaccine formulation, the adjusted VE was 54.9% (95%CI: 38.9, 66.9%). VE appeared to be much higher during high versus low influenza activity periods. The adjusted point estimate for VE was highest in the 18-49 year age group (76.6%) followed by 6-23 months (58.1%) and 2-17 years (52.5%). Adjusted estimates were not done for those ≥50 years of age due to small numbers. VE in patients with underlying disease was 75.5% compared to 48.0% in those without. Our findings demonstrate moderate protection by influenza vaccination and support the utility of influenza vaccination in the tropics including in very young children and those with underlying disease.