Non-specific effects of the inactivated influenza vaccine. A test-negative study: The inactivated influenza vaccine and SARS-CoV-2 infections

BACKGROUND

Previous research suggested that the inactivated influenza vaccine (IIV) may protect against SARS-CoV-2 infection or a severe course of COVID-19. These findings were however based on cohort studies, that are prone to confounding by indication. We examined the association between IIV and SARS-Cov-2 infection in a Dutch population using a test-negative design.

METHODS

This test-negative case-control study was conducted in adults (≥60) who tested because of COVID-19 like symptoms at community SARS-CoV-2 testing locations in the Netherlands during the period of November 8th 2021-March 11th 2022. Information on receipt of IIV in October-November 2021 was routinely collected at each visit. Logistic regression was used to calculate unadjusted, partially (sex, age, education level) and fully adjusted (COVID-19 vaccination, IIV 2020) odds ratios (ORs) for receipt of IIV in SARS-CoV-2 positive versus negative subjects. Differential effects on SARS-CoV-2 risk by time since IIV were investigated by including an interaction term for calendar time: November 2021-January 2022 vs February-March 2022.

RESULTS

In total, 1,832 participants were included in the main analysis, of whom 336 (18.3 %) had a positive SARS-CoV-2 test. No significant association between IIV and SARS-CoV-2 infection was found; fully adjusted OR of 1.07 (95 % CI: 0.78-1.49). The interaction term for time periods was not significant (1.04 [95 % CI: 0.51-2.15], p = 0.91). Results were robust in sensitivity analyses.

CONCLUSIONS

While earlier observational studies suggested a protective non-specific effect of IIV and SARS-CoV-2 infections, this smaller, but well controlled test-negative design study does not suggest an effect, either positive or negative. Larger test-negative design studies, or alternative designs such as the self-controlled case series design are needed to confirm these findings and provide more definite answers on the topic.

Real-world effectiveness of seasonal influenza vaccination and age as effect modifier: A systematic review, meta-analysis and meta-regression of test-negative design studies

BACKGROUND

Under the global risk of epidemic rebound of influenza after COVID-19 outbreak, the study aimed to provide a comprehensive evaluation of the seasonal influenza vaccine effectiveness (IVE) and to explore the potential effect modifiers.

METHODS

We searched for test-negative design studies with IVE estimates published between January 1, 2017 and December 31, 2022. We estimated pooled IVE using random-effects meta-analysis, and conducted meta-regression with study site, age, sex and comorbidity as explanatory variables.

RESULTS

We identified 2429 publications and included 191 in the meta-analysis. The pooled IVE was 41.4 % (95 % CI: 39.2-43.5 %) against any influenza. For specific strains, the IVE was 55.4 % (95 % CI: 52.7-58.1 %) against A/H1N1, 26.8 % (95 % CI: 23.5-29.9 %) against A/H3N2, 47.2 % (95 % CI: 38.1-54.9 %) against B/Yamagata, and 40.6 % (95 % CI: 23.7-53.7 %) against B/Victoria, and the effectiveness against A/H3N2 was significantly lower than A/H1N1 (p < 0.0001) and B/Yamagata (p < 0.0001). The pooled IVE was 39.2 % (95 % CI: 36.5-41.9 %) in preventing influenza-associated outpatient visit and 43.7 % (95 % CI: 39.7-47.4 %) in preventing influenza-related hospitalization. The IVE against any influenza was 48.6 % (95 % CI: 44.7-52.2 %) for children aged < 18 years, 36.7 % (95 % CI: 31.9-41.1 %) for adults aged 18-64 years, and 30.6 % (95 % CI: 26.2-34.8 %) for elderly aged ≥65 years. Meta-regression revealed that the IVE was associated with the average age of study participants, in which both young adults [relative odds ratio (ROR) = 1.225, 95 % confidence interval (CI): 1.099-1.365, p = 0.0002] and elderly (ROR = 1.245, 95 % CI: 1.083-1.431, p = 0.002) manifested a significantly decreased effectiveness compared with children.

CONCLUSIONS

Influenza vaccines provided moderate protection against laboratory-confirmed influenza and related outpatient visit and hospitalization. However, the effectiveness may vary substantially by virus type and age group, suggesting the necessity to tailor vaccination strategies especially for older individuals and against the A/H3N2 strain, and to promote annual immunization and annual analysis of vaccine effectiveness.

Effectiveness of 13-valent pneumococcal conjugate vaccine against vaccine-serotype community acquired pneumococcal diseases among children in China: A test-negative case-control study

BACKGROUND

In 2016, China licensed 13-valent pneumococcal conjugate vaccine (PCV13) based on a study that demonstrated its immunogenicity is non-inferior to PCV7. However, the real-world effectiveness of PCV13 against vaccine-serotype pneumococcal diseases in China has limited evidence.

METHODS

A test-negative case-control study was conducted among children under 5 years old admitted to the Children's Hospital of Soochow University (SCH) with respiratory tract infections from January 2018 to December 2020. Cases were defined as children from whom the isolates were tested positive for Streptococcus pneumoniae (S. pneumoniae) with serotypes included in PCV13. Two control groups were included, one represented children with isolates positive for S. pneumoniae of non-PCV13 serotypes and the other comprised children who tested negative for S. pneumoniae. The S. pneumoniae-negative controls were selected by matching them to the cases based on gender, age and admission date in a 1:1 ratio. Vaccine effectiveness (VE) was calculated using a logistic regression model as (1- adjusted odds ratio) * 100 %.

RESULTS

A total of 2371 pneumococcal isolates were included in the analysis, of which 75.0 % (1779/2371) were covered by PCV13 serotypes. Consequently, these 1779 children were classified as cases, and 592 children were designated as non-PCV13 serotype controls. Another 1779 children were correspondingly recruited as S. pneumoniae-negative controls. Overall, 40 cases (2.3 %) and 148 controls (6.2 %) had received vaccination. The overall VE in the PCV13/non-PCV13 serotypes case-control study was 50.0 % (95 % CI: 15.0, 70.7), which was lower than the VE of 74.4 % (95 % CI: 60.7, 83.3) in the matched PCV13/S. pneumoniae-negative case-control study. VE was higher for ≥ 2 or ≥ 3 doses of vaccination compared to ≥ 1 dose. VE against specific PCV13 serotypes (6B, 6A and 19F) was higher than for other serotypes.

CONCLUSIONS

PCV13 vaccination demonstrates effectiveness against vaccine-serotype pneumococcal diseases in children, particularly for serotypes 6B, 6A and 19F.

Test negative design for vaccine effectiveness estimation in the context of the COVID-19 pandemic: A systematic methodology review

BACKGROUND

During the height of the global COVID-19 pandemic, the test-negative design (TND) was extensively used in many countries to evaluate COVID-19 vaccine effectiveness (VE). Typically, the TND involves the recruitment of care-seeking individuals who meet a common clinical case definition. All participants are then tested for an infection of interest.

OBJECTIVES

To review and describe the variation in TND methodology, and disclosure of potential biases, as applied to the evaluation of COVID-19 VE during the early vaccination phase of the pandemic.

METHODS

We conducted a systematic review by searching four biomedical databases using defined keywords to identify peer-reviewed articles published between January 1, 2020, and January 25, 2022. We included only original articles that employed a TND to estimate VE of COVID-19 vaccines in which cases and controls were evaluated based on SARS-CoV-2 laboratory test results.

RESULTS

We identified 96 studies, 35 of which met the defined criteria. Most studies were from North America (16 studies) and targeted the general population (28 studies). Outcome case definitions were based primarily on COVID-19-like symptoms; however, several papers did not consider or specify symptoms. Cases and controls had the same inclusion criteria in only half of the studies. Most studies relied upon administrative or hospital databases assembled for a different (non-evaluation) clinical purpose. Potential unmeasured confounding (20 studies), misclassification of current SARS-CoV-2 infection (16 studies) and selection bias (10 studies) were disclosed as limitations by some studies.

CONCLUSION

We observed potentially meaningful deviations from the validated design in the application of the TND during the COVID-19 pandemic.

Immune escape and waning immunity of COVID-19 monovalent mRNA vaccines against symptomatic infection with BA.1/BA.2 and BA.5 in Japan

BACKGROUND

Repeated emergence of variants with immune escape capacity and waning immunity from vaccination are major concerns for COVID-19. We examined whether the surge in Omicron subvariant BA.5 cases was due to immune escape or waning immunity through vaccine effectiveness (VE) evaluation.

METHODS

A test-negative case-control study was conducted in 16 clinics/hospitals during the BA.1/BA.2-dominant and BA.5-dominant periods. VE against symptomatic infection was estimated after adjusting for age, sex, comorbidity, occupation, testing frequency, prior infection, close contact history, clinic/hospital, week, and preventive measures. Absolute VE (aVE) was calculated for 2/3/4 doses, compared to the unvaccinated. Relative VE (rVE) was calculated, comparing 3 vs 2 and 4 vs 3 doses.

RESULTS

13,025 individuals were tested during the BA.1/BA.2-dominant and BA.5-dominant periods with similar baseline characteristics. For BA.1/BA.2, aVE was 52 % (95 %CI:34-66) 14 days-3 months post-dose 2, 42 % (29-52) > 6 months post-dose 2, 71 % (64-77) 14 days-3 months post-dose 3, and 68 % (52-79) 3-6 months post-dose 3. rVE was 49 % (38-57) 14 days-3 months post-dose 3 and 45 % (18-63) 3-6 months post-dose 3. For BA.5, aVE was 56 % (27-73) 3-6 months post-dose 2, 32 % (12-47) > 6 months post-dose 2, 70 % (61-78) 14 days-3 months post-dose 3, 59 % (48-68) 3-6 months post-dose 3, 50 % (29-64) > 6 months post-dose 3, and 74 % (61-83) ≥ 14 days post-dose 4. rVE was 56 % (45-65) 14 days-3 months post-dose 3, 39 % (27-48) 3-6 months post-dose 3, 25 % (-2-45) > 6 months post-dose 3, and 30 % (-6-54) ≥ 14 days post-dose 4.

CONCLUSIONS

Booster doses initially provided high protection against BA.5 at a level similar to that against BA.1/BA.2. However, the protection seemed shorter-lasting against BA.5, which likely contributed to the surge. Furthermore, rVE post-dose 4 was low even among recent vaccinees. These results support the introduction of variant-containing vaccines and emphasize the need for vaccines with longer duration of protection.

Influenza vaccine effectiveness against influenza A during the delayed 2022/23 epidemic in Shihezi, China

After the temporary end of COVID-19 in China in February 2023, the influenza epidemic peaked in March across many Chinese places. We recruited a total of 258 all-age subjects presenting influenza-like illness (ILI) in Shihezi city, China from January 1 to March 16, 2023, and tested for influenza virus infection. Using a test-negative design, we assessed influenza vaccine effectiveness (VE) of 56.3% (95% CrI: 13.6, 73.6) against medically attended, influenza illness during the delayed 2022/23 influenza epidemic. The findings contributed to the continuous monitoring of the influenza vaccine performance across the world, especially in the "post-COVID" pandemic era.

Effectiveness of inactivated influenza and COVID-19 vaccines in hospitalized children in 2022/23 season in Japan - The first season of co-circulation of influenza and COVID-19

We have analyzed the inactivated vaccine effectiveness (VE)for preventing influenza hospitalization by test-negative design in the 2022/23 season. This is the first season of co-circulation of influenza and COVID-19, and a unique period because all inpatients received COVID-19 screening. Among 536 children hospitalized with fever, none were positive for both influenza and SARS-CoV-2. The adjusted VE for preventing influenza A for all children, the 6-12-year-old group, and those with underlying diseases was 34 % (95 ％CI, -16 %-61 %, n = 474), 76 % (95 ％ CI, 21 %-92 %, n = 81), and 92 % (95 ％ CI, 30 %-99 %, n = 86), respectively. Only 1 out of 35 hospitalized cases with COVID-19, and 42 out of 429 controls, had been immunized with COVID-19 vaccine. This is the first report showing influenza VE by age group in children in this limited season. We still recommend the inactivated influenza vaccine for children based on the significant VE in subgroup analysis.

Influenza vaccine viruses and the development of seasonal vaccines: A Japanese perspective

In Japan, the Ministry of Health, Labour and Welfare (MHLW) designates one specific virus strain for each component of the quadrivalent seasonal influenza vaccine, and four domestic manufacturers produce egg-based influenza vaccines with the same formulation (inactivated, split-virus) using uniform vaccine strains. Thus, discussions of the development of effective seasonal influenza vaccines so far has focused solely on the antigenic match between the vaccine strains and epidemic viruses. However, in 2017, the Japanese selection system of vaccine viruses demonstrated that even a candidate vaccine virus that is antigenically similar to the predicted circulating viruses is not necessarily suitable for vaccine production, given lower productivity of the vaccine. Taking this experience into account, the MHLW reformed the scheme of vaccine strain selection in 2018, and instructed the Vaccine Epidemiology Research Group created by the MHLW to probe how the virus strains for the seasonal influenza vaccine should be selected in Japan. In this context, a symposium, entitled "Issues of the Present Seasonal Influenza Vaccines and Future Prospects", was held as part of the 22nd Annual Meeting of the Japanese Society for Vaccinology in 2018, and subjects related to the influenza vaccine viruses were discussed among relevant administrators, manufacturers, and researchers. This report summarizes the presentations given at that symposium in order to convey the present scheme of vaccine virus selection, the evaluation of the resulting vaccines, and the efforts at new vaccine formulation in Japan. Notably, from March 2022, the MHLW has launched a discussion of the merits of the seasonal influenza vaccines produced by foreign manufacturers.

Influenza vaccine effectiveness in patients hospitalized with severe acute respiratory infection in Lithuania during the 2019-2020 influenza season: a test negative case - control study

BACKGROUND

Influenza is a contagious viral airborne disease that adds to the clinical and economic burden on the healthcare system. It could be prevented substantially by seasonal influenza vaccination. Seasonal influenza vaccine effectiveness (SIVE) varies a lot and should therefore be monitored. This report aims to update age-stratified SIVE estimates among patients hospitalized due to severe acute respiratory infection (SARI) during the 2019-2020 influenza season.

METHODS

We performed a test-negative case-control study between December 2019 and April 2020 influenza season. We estimated SIVE and its 95% confidence intervals (95% CI) with logistic regression as (1-odds ratio)*100%. The models were adjusted for covariates that changed the unadjusted SIVE by ≥ 10%.

RESULTS

Among 84 participants, 32 (38.1%) were influenza positive, mostly with A(H1N1)pdm09 (25 cases; 78.1%). SIVE against any influenza adjusted for age and heart disease was 39.2% (95% CI: -119.3%, 83.1%). Age-stratified point estimates adjusted for heart diseases indicated different SIVE, and were 64.0% (95% CI: -309.2%, 96.8%) and 21.6% (95% CI: -252.2%, 82.6%) for 18-64 and ≥ 65 year-old participants, respectively.

CONCLUSIONS

The point estimates suggested low to moderate SIVE against any influenza among hospitalized 18-64-year-old SARI participants, while low estimates were found in the ≥ 65-year-old group. Although broad SIVE confidence intervals indicate a small sample size and therefore the results can serve only as indicatory, they are in line with the estimates reported by other studies during the 2019-2020 season.

Addressing misclassification bias in vaccine effectiveness studies with an application to Covid-19

Safe and effective vaccines are crucial for the control of Covid-19 and to protect individuals at higher risk of severe disease. The test-negative design is a popular option for evaluating the effectiveness of Covid-19 vaccines. However, the findings could be biased by several factors, including imperfect sensitivity and/or specificity of the test used for diagnosing the SARS-Cov-2 infection. We propose a simple Bayesian modeling approach for estimating vaccine effectiveness that is robust even when the diagnostic test is imperfect. We use simulation studies to demonstrate the robustness of our method to misclassification bias and illustrate the utility of our approach using real-world examples.

Effectiveness of Covid-19 vaccines against symptomatic and asymptomatic SARS-CoV-2 infections in an urgent care setting

BACKGROUND

It is critical to monitor changes in vaccine effectiveness against COVID-19 outcomes for various vaccine products in different population subgroups.

METHODS

We conducted a retrospective study in patients ≥12 years who underwent testing for SARS-CoV-2 virus from April 14 through October 25, 2021, at urgent care centers in the New York metropolitan area. Patients self-reported vaccination status at the time of testing. We used a test-negative design to estimate vaccine effectiveness (VE) by comparing odds of a positive test for SARS-CoV-2 infection among vaccinated (n = 474,805), partially vaccinated (n = 87,834), and unvaccinated (n = 369,333) patients, adjusted for demographic factors and calendar time.

RESULTS

VE against symptomatic infection after 2 doses of mRNA vaccine was 96% (95% Confidence Interval: 95%, 97%) in the pre-delta period and reduced to 79% (95% CI: 77%, 81%) in the delta period. In the delta period, VE for 12-15-year-olds (85%; [95% CI: 81%, 88%]) was higher compared to older age groups (<65% for all other age groups). VE estimates did not differ by sex and race/ethnicity. VE against symptomatic infection was the highest for individuals with a prior infection followed by full vaccination. VE against symptomatic infection after the 2-dose mRNA-1273 vaccine (82% [95% CI: 80%, 84%]) was higher compared to the BNT162b2 vaccine (76% [95% CI: 74%, 78%]) in the delta period. VE after 1-dose of the Ad26.COV2.S vaccine was the lowest compared to other vaccines (19% [95% CI: 15%, 23%]) in the delta period.

CONCLUSIONS

VE against infection after two doses of the mRNA vaccines was high initially, but significantly reduced against the delta variant for both FDA-approved vaccines.

A comparison of the test-negative and the matched case-control study designs for estimation of EV71 vaccine immunological surrogate endpoints from a randomized controlled trial

Since TND could be an appropriate method to assess vaccine effectiveness, we want to know whether it may be used for the estimation of vaccine immunological surrogate endpoints, like case-control study. We conducted two study designs (test-negative design (TND) VS matched case-control design (MCC)) to evaluate immunological surrogate endpoint against EV71-associated diseases. We calculated sensitivity (proportion of participants with EV71-associated disease who have a titer less than the cutoff at day 56), specificity (proportion of matched controls who have a titer equal or greater than the cutoff at day 56), and corresponding Youden index ([sensitivity + specificity] − 1). Then, we compared them between TND and MCC. In test-negative design, we totally enrolled 7029 subjects, 49 tested positive as cases and 6980 tested negative as controls in per-protocol population. In matched case-control design, we totally enrolled 305 subjects, 51 as cases, and 254 as controls in whole cohort. In sensitivity and specificity comparison, TND and MCC’s results were similar to each other, except for a titer of 1:4. Nonetheless, in Youden index comparison, MCC’s results were slightly higher than the TND’s, except for a titer of 1:4. EV71 vaccine immunological surrogate endpoints derived from TND was similar to MCC’s. Our results supported that TND could become an alternative research design with the progress of surveillance.

Vaccine effectiveness and duration of protection against symptomatic infections and severe Covid-19 outcomes in adults aged 50 years and over, France, January to mid-December 2021

Background

SARS-CoV-2 continues to spread despite fast vaccine rollout, which could be attributed to waning immunity or to a reduced protection against some variants. A thorough characterization of vaccine protection and its duration in time is needed to inform vaccination policies and enhance public trust.

Methods

We linked three national databases with exhaustive information on screening, vaccination and hospitalizations in France from January 1st to December 12, 2021. We performed a two-step analysis to estimate vaccine effectiveness against severe outcomes of Covid-19 (requiring hospitalization) in people aged 50 years or over, combining: (i) a test-negative case-control design to assess vaccine effectiveness against symptomatic infections; and (ii) a survival analysis to assess the additional protection against severe outcomes (hospitalizations, ICU admissions and inpatient deaths) in infected individuals.

Findings

We found a high vaccine effectiveness in people aged 50 years or more, reaching 82% against symptomatic infections and 94% against hospitalizations, after a full vaccination scheme with the Covid-19 vaccines used in France.Vaccine effectiveness against symptomatic infections decreased over time, dropping to 53% after six months, but remained high against severe outcomes (90% after six months). The booster dose allowed restoring protection levels above 90% against symptomatic infections. Vaccine protection and its evolution in time, showed little difference against the variants that circulated prior to December 2021 in France, including the Delta variant.

Interpretation

Though vaccine immunity decreases over time, vaccination remains crucial to provide individual protection against severe outcomes requiring hospitalization. This decline can be reversed by the receipt of a booster dose.

Effectiveness of Covishield vaccine in preventing Covid-19 - A test-negative case-control study

INTRODUCTION

This study aimed at assessing the vaccine effectiveness (VE) of Covishield, which is identical to AstraZeneca vaccine, in preventing laboratory-confirmed Covid-19.

METHODS

Using test-negative case-control design, information on vaccination status of cases with Covid-19 among healthcare workers in our institution in Puducherry, India, and an equal number of controls matched for age and date of testing, was obtained. The groups were compared using multivariable conditional logistic regression to calculate odds ratios (OR). VE was calculated as 100*(1-adjusted odds ratio)%.

RESULTS

Using data from 360 case-control pairs, VE of one dose and of two doses, in providing protection against Covid-19 was 49% (95% CI: 17%-68%) and 54% (27%-71%), respectively. Among cases with moderately severe disease that required oxygen therapy, VE following any number of vaccine doses was 95% (44%-100%).

CONCLUSION

Covishield vaccine protected significantly against Covid-19, with a higher protection rate against severe forms of disease.

Association between vaccination status, symptom identification and healthcare use: Implications for test negative design observational studies

AIM

To test the internal validity of the test-negative design (TND) by investigating associations between maternal influenza vaccination, and new virus detection episodes (VDEs), acute respiratory illness, and healthcare visits in their children.

METHODS

Eighty-five children from a birth cohort provided daily symptoms, weekly nasal swabs, and healthcare use data until age 2-years. Effect estimates are summarised as incidence rate ratios (IRR).

RESULTS

There was no association between maternal vaccination and VDEs in children (IRR = 1.1; 95 %CI = 0.9-1.2). Influenza-vaccinated mothers were more likely than unvaccinated mothers to both report, and seek healthcare for, acute lower respiratory illness in their children, IRR = 2.4; 95 %CI = 1.2-4.8 and IRR = 2.2; 95 %CI = 1.1-4.3, respectively.

CONCLUSION

A key assumption of the TND, that healthcare seeking behaviour for conditions of the same severity is not associated with vaccine receipt, did not hold. Further studies of the performance of the TND in different populations are required to confirm its validity.

Potential test-negative design study bias in outbreak settings: application to Ebola vaccination in Democratic Republic of Congo

BACKGROUND

Infectious disease outbreaks present unique challenges to study designs for vaccine evaluation. Test-negative design (TND) studies have previously been used to estimate vaccine effectiveness and have been proposed for Ebola virus disease (EVD) vaccines. However, there are key differences in how cases and controls are recruited during outbreaks and pandemics of novel pathogens, whcih have implications for the reliability of effectiveness estimates using this design.

METHODS

We use a modelling approach to quantify TND bias for a prophylactic vaccine under varying study and epidemiological scenarios. Our model accounts for heterogeneity in vaccine distribution and for two potential routes to testing and recruitment into the study: self-reporting and contact-tracing. We derive conventional and hybrid TND estimators for this model and suggest ways to translate public health response data into the parameters of the model.

RESULTS

Using a conventional TND study, our model finds biases in vaccine effectiveness estimates. Bias arises due to differential recruitment from self-reporting and contact-tracing, and due to clustering of vaccination. We estimate the degree of bias when recruitment route is not available, and propose a study design to eliminate the bias if recruitment route is recorded.

CONCLUSIONS

Hybrid TND studies can resolve the design bias with conventional TND studies applied to outbreak and pandemic response testing data, if those efforts collect individuals' routes to testing. Without route to testing, other epidemiological data will be required to estimate the magnitude of potential bias in a conventional TND study. Since these studies may need to be conducted retrospectively, public health responses should obtain these data, and generic protocols for outbreak and pandemic response studies should emphasize the need to record routes to testing.

An evaluation of a test-negative design for EV-71 vaccine from a randomized controlled trial

Background: The test-negative design has been used widely in evaluation of various vaccines' effectiveness, such as influenza, rotavirus, and so on. Recently, there have been some studies about EV-71 vaccine effectiveness by using test-negative design(TND). However, the validity of the TND application in EV-71 vaccines has not been evaluated.Methods: This study is set upon prior methods to evaluate the validity of TND for influenza vaccine by using a randomized controlled clinical trial database. Vaccine effectiveness estimated by TND (VE-TND) in modified intention-to-treat population (mITT) and per-protocol-set population(PPS) was derived from a large randomized placebo-controlled clinical trial (RCT) of inactivated monovalent EV-71 vaccine in China. Derived VE-TND estimates were compared to the original vaccine efficacy results in RCT (VE-RCT).Results: We totally enrolled 7325 participants who seeked medical care for suspected EV-71 infected diseases during the surveillance. There are no significant differences between cases(test-positive) and controls(test-negative) on sex, age, height, and weight. TND vaccine effectiveness estimates were similar to original RCT vaccine efficacy estimates, both in modified intention-to-treat population and per-protocol populations.Conclusions: This study supports that TND, as an appropriate observational study design is valid to measure EV-71 vaccine effectiveness.

Brand-specific influenza vaccine effectiveness estimates during 2019/20 season in Europe - Results from the DRIVE EU study platform

DRIVE (Development of Robust and Innovative Vaccine Effectiveness) is an IMI funded public-private platform that aims to annually estimate brand-specific influenza vaccine effectiveness (IVE), for public health and regulatory purposes. IVE analyses and reporting are conducted by public partners in the consortium. In 2019/20, four primary care-based test-negative design (TND) studies (Austria, England, Italy (n = 2)), eight hospital-based TND studies (Finland, France, Italy, Romania, Spain (n = 4)), and one population-based cohort study (Finland) were conducted. The COVID-19 pandemic affected influenza surveillance in all participating study sites, therefore the study period was truncated on February 29, 2020. Age-stratified (6 m-17y, 18-64y, ≥65y), confounder-adjusted, site-specific adjusted IVE estimates were calculated and pooled through meta-analysis. Parsimonious confounder-adjustment was performed, adjusting the estimates for age, sex and calendar time. TND studies included 3531 cases (351 vaccinated) and 5546 controls (1415 vaccinated) of all ages. IVE estimates were available for 8/11 brands marketed in Europe in 2019. Most children and adults < 64y were captured in primary care setting and the most frequently observed vaccine brand was Vaxigrip Tetra. The estimate against any influenza for Vaxigrip Tetra in primary care setting was 61% (95%CI 38-77) in children and 32% (95%CI -13-59) in adults up to 64y. Most adults ≥ 65y were captured in hospital setting and the most frequently observed brand was Fluad, with an estimate of 52% (95%CI 27-68). The population-based cohort covered 511,854 person-years and two vaccine brands. In children aged 2-6y, the IVE against any influenza was 68% (95%CI 58-75) for Fluenz Tetra and 71% (56-80) for Vaxigrip Tetra. In adults ≥ 65y, IVE against any influenza was 29% (20-36) for Vaxigrip Tetra. DRIVE is a growing platform. Public health institutes with surveillance data and hospitals in countries with high influenza vaccine coverage are encouraged to join DRIVE.

Variable seasonal influenza vaccine effectiveness across geographical regions, age groups and levels of vaccine antigenic similarity with circulating virus strains: A systematic review and meta-analysis of the evidence from test-negative design studies after the 2009/10 influenza pandemic

BACKGROUND

We examined the influence of some factors on seasonal influenza vaccine effectiveness (VE) from test-negative design (TND) studies.

METHODS

We systematically searched for full-text publications of VE against laboratory-confirmed influenza from TND studies in outpatient settings after the 2009/10 influenza pandemic. Two reviewers independently selected and extracted data from the included studies. We calculated pooled adjusted VE across geographical regions, age groups and levels of vaccine antigenic similarity with circulating virus strains, using an inverse variance, random-effects model.

RESULTS

We included 76 full-text articles from 11,931 citations. VE estimates against A(H1N1)pdm09, A(H3N2), influenza B, and all influenza were homogenous and point pooled VE higher in the Southern hemisphere compared with the Northern hemisphere. The difference in pooled VE between the Southern and Northern hemispheres was statistically significant for A(H3N2), influenza B, and all influenza. A consistent pattern was observed in pooled VE across both hemispheres and continents, with the highest point pooled VE being against A(H1N1)pdm09, followed by influenza B, and lowest against A(H3N2). A nearly consistent pattern was observed in pooled VE across age groups in the Northern hemisphere, with pooled VE mostly decreasing with age. Point pooled VE against A(H3N2), influenza B, and all influenza were statistically significantly higher when vaccine was antigenically similar to circulating virus strains compared with when antigenically dissimilar. Similar pattern was observed in the Northern hemisphere, but there was a lack of data from the Southern hemisphere.

CONCLUSION

Consistent patterns appear to exist in seasonal influenza VE across regions, age groups, and levels of vaccine antigenic similarity with circulating virus strains, with best vaccine performance against A(H1N1)pdm09 and worst against A(H3N2). The evidence highlights the need to consider geographical location, age, and vaccine antigenic similarity with circulating virus strains when designing and evaluating influenza VE studies.

Association between autoimmune diseases and COVID-19 as assessed in both a test-negative case-control and population case-control design

Background

COVID-19 epidemic has paralleled with the so called infodemic, where countless pieces of information have been disseminated on putative risk factors for COVID-19. Among those, emerged the notion that people suffering from autoimmune diseases (AIDs) have a higher risk of SARS-CoV-2 infection.

Methods

The cohort included all COVID-19 cases residents in the Agency for Health Protection (AHP) of Milan that, from the beginning of the outbreak, developed a web-based platform that traced positive and negative cases as well as related contacts. AIDs subjects were defined ad having one the following autoimmune disease: rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, Sjogren disease, ankylosing spondylitis, myasthenia gravis, Hashimoto’s disease, acquired autoimmune hemolytic anemia, and psoriatic arthritis. To investigate whether AID subjects are at increased risk of SARS-CoV-2 infection, and whether they have worse prognosis than AIDs-free subjects once infected, we performed a combined analysis of a test-negative design case–control study, a case–control with test-positive as cases, and one with test-negative as cases (CC-NEG).

Results

During the outbreak, the Milan AHP endured, up to April 27th 2020, 20,364 test-positive and 34,697 test-negative subjects. We found no association between AIDs and being positive to COVID-19, but a statistically significant association between AIDs and being negative to COVID-19 in the CC-NEG. If, as likely, test-negative subjects underwent testing because of respiratory infection symptoms, these results imply that autoimmune diseases may be a risk factor for respiratory infections in general (including COVID-19), but they are not a specific risk factor for COVID-19. Furthermore, when infected by SARS-CoV-2, AIDs subjects did not have a worse prognosis compared to non-AIDs subjects. Results highlighted a potential unbalance in the testing campaign, which may be correlated to the characteristics of the tested person, leading specific frail population to be particularly tested.

Conclusions

Lack of availability of sound scientific knowledge inevitably lead unreliable news to spread over the population, preventing people to disentangle them form reliable information. Even if additional studies are needed to replicate and strengthen our results, these findings represent initial evidence to derive recommendations based on actual data for subjects with autoimmune diseases.

Update to the AWED (Applying Wolbachia to Eliminate Dengue) trial study protocol: a cluster randomised controlled trial in Yogyakarta, Indonesia

BACKGROUND

The AWED (Applying Wolbachia to Eliminate Dengue) trial is a parallel, two-arm, non-blinded cluster randomised controlled trial that is under way in Yogyakarta, Indonesia, with the aim of measuring the efficacy of Wolbachia-infected Aedes aegypti deployments in reducing dengue incidence in an endemic setting. Enrolment began in January 2018 and is ongoing. The original study protocol was published in April 2018. Here, we describe amendments that have been made to the study protocol since commencement of the trial.

METHODS

The key protocol amendments are (1) a revised study duration with planned end of participant enrolment in August 2020, (2) the addition of new secondary objectives (i) to estimate serotype-specific efficacy of the Wolbachia intervention and (ii) to compare Ae. aegypti abundance in intervention versus untreated clusters, (3) an additional exposure classification for the per-protocol analysis where the Wolbachia exposure index is calculated using only the cluster-level Wolbachia prevalence in the participant's cluster of residence, (4) power re-estimation using a multinomial sampling method that better accounts for randomness in sampling, and (5) the addition of two trial stopping rules to address the potential for persistently low rates of virologically confirmed dengue case enrolment and Wolbachia contamination into untreated clusters. Additional minor changes to the protocol are also described.

DISCUSSION

The findings from this study will provide the first experimental evidence for the efficacy of Wolbachia in reducing dengue incidence. Enrolment in the trial will conclude this year (2020) and results will be reported shortly thereafter.

TRIAL REGISTRATION

ClinicalTrials.gov, identifier: NCT03055585. Registered on 14 February 2017. Last updated 22 March 2020.

Analysis of cluster-randomized test-negative designs: cluster-level methods

Intervention trials of vector control methods often require community level randomization with appropriate inferential methods. For many interventions, the possibility of confounding due to the effects of health-care seeking behavior on disease ascertainment remains a concern. The test-negative design, a variant of the case-control method, was introduced to mitigate this issue in the assessment of the efficacy of influenza vaccination (measured at an individual level) on influenza infection. Here, we introduce a cluster-randomized test-negative design that includes randomization of the intervention at a group level. We propose several methods for estimation and inference regarding the relative risk (RR). The inferential methods considered are based on the randomization distribution induced by permuting intervention assignment across two sets of randomly selected clusters. The motivating example is a current study of the efficacy of randomized releases of Wolbachia-infected Aedes aegypti mosquitoes to reduce the incidence of dengue in Yogyakarta City, Indonesia. Estimation and inference techniques are assessed through a simulation study.

Evaluating the effectiveness of the influenza vaccine during respiratory outbreaks in Singapore's long term care facilities, 2017

Influenza outbreaks occur periodically in Long Term Care Facilities (LTCFs) and vaccination is critical in preventing influenza infections. We evaluated the influenza vaccine effectiveness (VE) during respiratory outbreaks in LTCFs reported to the Ministry of Health, Singapore in 2017. A test-negative design was used to estimate the ratio of the odds of testing positive for influenza among vaccinated individuals to the odds among unvaccinated individuals. The VE was calculated as (1-odds ratio) × 100%. For adjusted VE, the estimates were derived using logistic regression adjusted for age group, gender, month of illness, and number of days from date of illness onset till to swab collection date. Estimates by influenza subtypes and post-vaccination time periods (15-180 days & 181-365 days) were also calculated using stratified data. 264 individuals, with 118 laboratory-confirmed influenza cases [32 A(H1N1)pdm09, 75 A(H3N2), 11 A(untypable)], were included in the analysis. No one was identified to be infected with influenza B. The overall adjusted VE estimate was 40.5% (95% CI: -12.2-68.5%), while the subtype-specific adjusted VE estimates were -43.4% (95% CI: -312.4-50.2%) against A(H1N1)pdm09 and 57.1% (95% CI: 5.7-80.5%) against A(H3N2). At 15-180 days post-vaccination period, the adjusted VEs were 59.3% (95% CI: 18.0-79.8%) against all influenza, 35.4% (95% CI: -123.5-81.3%) against A(H1N1)pdm09 and 67.9% (95% CI: 22.5-86.7%) against A(H3N2). Estimates were not significant at 181-365 days post-vaccination. The influenza vaccine showed varying effectiveness among individuals in Singapore's LTCFs in 2017, with a higher effectiveness among those who were more recently vaccinated. It remains an important tool in preventing influenza infections, especially for those who are at high risk of influenza-related complications.

Effect of propensity of seeking medical care on the bias of the estimated effectiveness of rotavirus vaccines from studies using a test-negative case-control design

BACKGROUND

Rotavirus is the leading cause of severe diarrhea among children worldwide, and vaccines can reduce morbidity and mortality by 50-98%. The test-negative control (TNC) study design is increasingly used for evaluating the effectiveness of vaccines against rotavirus and other vaccine-preventable diseases. In this study design, symptomatic patients who seek medical care are tested for the pathogen of interest. Those who test positive (negative) are classified as cases (controls).

METHODS

We use a probability model to evaluate the bias of estimates of rotavirus vaccine effectiveness (VE) against rotavirus diarrhea resulting in hospitalization in the presence of possible confounding and selection biases due to differences in the propensity of seeking medical care (PSMC) between vaccinated and unvaccinated children.

RESULTS

The TNC-based VE estimate corrects for confounding bias when the confounder's effects on the probabilities of rotavirus and non-rotavirus related hospitalizations are equal. If this condition is not met, then the estimated VE may be substantially biased. The bias is more severe in low-income countries, where VE is known to be lower. Under our model, differences in PSMC between vaccinated and unvaccinated children do not result in selection bias when the TNC study design is used.

CONCLUSIONS

In practice, one can expect the association of PSMC (or other potential confounders) with the probabilities of rotavirus and non-rotavirus related hospitalization to be similar, in which case the confounding effects will only result in small bias in the VE estimate from TNC studies. The results of this work, along with those of our previous paper, confirm the TNC design can be expected to provide reliable estimates of rotavirus VE in both high- and low-income countries.

Intraseason decline in influenza vaccine effectiveness during the 2016 southern hemisphere influenza season: A test-negative design study and phylogenetic assessment

BACKGROUND

We estimated the effectiveness of seasonal inactivated influenza vaccine and the potential influence of timing of immunization on vaccine effectiveness (VE) using data from the 2016 southern hemisphere influenza season.

METHODS

Data were pooled from three routine syndromic sentinel surveillance systems in general practices in Australia. Each system routinely collected specimens for influenza testing from patients presenting with influenza-like illness. Next generation sequencing was used to characterize viruses. Using a test-negative design, VE was estimated based on the odds of vaccination among influenza-positive cases as compared to influenza-negative controls. Subgroup analyses were used to estimate VE by type, subtype and lineage, as well as age group and time between vaccination and symptom onset.

RESULTS

A total of 1085 patients tested for influenza in 2016 were included in the analysis, of whom 447 (41%) tested positive for influenza. The majority of detections were influenza A/H3N2 (74%). One-third (31%) of patients received the 2016 southern hemisphere formulation influenza vaccine. Overall, VE was estimated at 40% (95% CI: 18-56%). VE estimates were highest for patients immunized within two months prior to symptom onset (VE: 60%; 95% CI: 26-78%) and lowest for patients immunized >4 months prior to symptom onset (VE: 19%; 95% CI: -73-62%).

DISCUSSION

Overall, the 2016 influenza vaccine showed good protection against laboratory-confirmed infection among general practice patients. Results by duration of vaccination suggest a significant decline in effectiveness during the 2016 influenza season, indicating immunization close to influenza season offered optimal protection.

The 2015-2016 influenza epidemic in Beijing, China: Unlike elsewhere, circulation of influenza A(H3N2) with moderate vaccine effectiveness

BACKGROUND

While the 2015-2016 influenza season in the northern hemisphere was dominated by A(H1N1)pdm09 and B/Victoria viruses, in Beijing, China, there was also significant circulation of influenza A(H3N2) virus. In this report we estimate vaccine effectiveness (VE) against influenza A(H3N2) and other circulating viruses, and describe further characteristics of the 2015-2016 influenza season in Beijing.

METHODS

We estimated VE of the 2015-2016 trivalent inactivated vaccine (TIV) against laboratory-confirmed influenza virus infection using the test-negative study design. The effect of prior vaccination on current VE was also examined.

RESULTS

Of 11,000 eligible patients included in the study, 2969 (27.0%) were influenza positive. Vaccination coverage was 4.2% in both cases and controls. Adjusted VE against all influenza was 8% (95% CI: -16% to 27%): 18% (95% CI: -38% to 52%) for influenza A(H1N1)pdm09, 54% (95% CI: 16% to 74%) for influenza A(H3N2), and -8% (95% CI: -40% to 18%) for influenza B/Victoria. The overall VE for receipt of 2015-2016 vaccination only, 2014-2015 vaccination only, and vaccinations in both seasons was -15% (95% CI: -63% to 19%), -25% (95% CI: -78% to 13%), and 18% (95% CI: -11% to 40%), respectively.

CONCLUSIONS

Overall the 2015-2016 TIV was protective against influenza infection in Beijing, with higher VE against the A(H3N2) viruses compared to A(H1N1)pdm09 and B viruses.

Basic principles of test-negative design in evaluating influenza vaccine effectiveness

Based on the unique characteristics of influenza, the concept of "monitoring" influenza vaccine effectiveness (VE) across the seasons using the same observational study design has been developed. In recent years, there has been a growing number of influenza VE reports using the test-negative design, which can minimize both misclassification of diseases and confounding by health care-seeking behavior. Although the test-negative designs offer considerable advantages, there are some concerns that widespread use of the test-negative design without knowledge of the basic principles of epidemiology could produce invalid findings. In this article, we briefly review the basic concepts of the test-negative design with respect to classic study design such as cohort studies or case-control studies. We also mention selection bias, which may be of concern in some countries where rapid diagnostic testing is frequently used in routine clinical practices, as in Japan.

On the bias of estimates of influenza vaccine effectiveness from test-negative studies

Estimates of the effectiveness of influenza vaccines are commonly obtained from a test-negative design (TND) study, where cases and controls are patients seeking care for an acute respiratory illness who test positive and negative, respectively, for influenza infection. Vaccine effectiveness (VE) estimates from TND studies are usually interpreted as vaccine effectiveness against medically-attended influenza (MAI). However, it is also important to estimate VE against any influenza illness (symptomatic influenza (SI)) as individuals with SI are still a public health burden even if they do not seek medical care. We present a numerical method to evaluate the bias of TND-based estimates of influenza VE with respect to MAI and SI. We consider two sources of bias: (a) confounding bias due to a (possibly unobserved) covariate that is associated with both vaccination and the probability of the outcome of interest and (b) bias resulting from the effect of vaccination on the probability of seeking care. Our results indicate that (a) VE estimates may suffer from substantial confounding bias when a confounder has a different effect on the probabilities of influenza and non-influenza ARI, and (b) when vaccination reduces the probability of seeking care against influenza ARI, then estimates of VE against MAI may be unbiased while estimates of VE against SI may be have a substantial positive bias.

Vaccine epidemiology: Its role in promoting sound immunization programs in Japan

In Japan, the Vaccine Epidemiology Research Group created by the Ministry of Health, Labour and Welfare has played an important role in demonstrating the solid scientific basis for vaccine efficacy and safety since 2002. Members of the group, including epidemiologists, clinicians and microbiologists, have been conducting collaborative studies on vaccines for influenza, pertussis, rotavirus gastroenteritis, polio and pneumonia. So far, the group has achieved several works and contributed to the national vaccination program, including research on the immunogenicity of low doses of influenza vaccine among young children, the immunogenicity and effectiveness of the 2009 influenza pandemic vaccine among various risk groups, the interchangeability of live/inactivated polio vaccines, the health impact of influenza on pregnant women, and the monitoring of influenza vaccine effectiveness using case-control studies with a test-negative design. As part of the 18th Annual Meeting of the Japanese Society of Vaccinology, these accomplishments were featured in the Vaccine Epidemiology Symposium. This report summarizes the recent epidemiological studies on vaccine in Japan as a prologue to the next six papers collected from the symposium.

Rotavirus vaccine effectiveness in low-income settings: An evaluation of the test-negative design

BACKGROUND

The test-negative design (TND), an epidemiologic method currently used to measure rotavirus vaccine (RV) effectiveness, compares the vaccination status of rotavirus-positive cases and rotavirus-negative controls meeting a pre-defined case definition for acute gastroenteritis. Despite the use of this study design in low-income settings, the TND has not been evaluated to measure rotavirus vaccine effectiveness.

METHODS

This study builds upon prior methods to evaluate the use of the TND for influenza vaccine using a randomized controlled clinical trial database. Test-negative vaccine effectiveness (VE-TND) estimates were derived from three large randomized placebo-controlled trials (RCTs) of monovalent (RV1) and pentavalent (RV5) rotavirus vaccines in sub-Saharan Africa and Asia. Derived VE-TND estimates were compared to the original RCT vaccine efficacy estimates (VE-RCTs). The core assumption of the TND (i.e., rotavirus vaccine has no effect on rotavirus-negative diarrhea) was also assessed.

RESULTS

TND vaccine effectiveness estimates were nearly equivalent to original RCT vaccine efficacy estimates. Neither RV had a substantial effect on rotavirus-negative diarrhea.

CONCLUSIONS

This study supports the TND as an appropriate epidemiologic study design to measure rotavirus vaccine effectiveness in low-income settings.

The European I-MOVE Multicentre 2013-2014 Case-Control Study. Homogeneous moderate influenza vaccine effectiveness against A(H1N1)pdm09 and heterogenous results by country against A(H3N2)

BACKGROUND

In the first five I-MOVE (Influenza Monitoring Vaccine Effectiveness in Europe) influenza seasons vaccine effectiveness (VE) results were relatively homogenous among participating study sites. In 2013-2014, we undertook a multicentre case-control study based on sentinel practitioner surveillance networks in six European Union (EU) countries to measure 2013-2014 influenza VE against medically-attended influenza-like illness (ILI) laboratory-confirmed as influenza. Influenza A(H3N2) and A(H1N1)pdm09 viruses co-circulated during the season.

METHODS

Practitioners systematically selected ILI patients to swab within eight days of symptom onset. We compared cases (ILI positive to influenza A(H3N2) or A(H1N1)pdm09) to influenza negative patients. We calculated VE for the two influenza A subtypes and adjusted for potential confounders. We calculated heterogeneity between sites using the I(2) index and Cochrane's Q test. If the I(2) was <50%, we estimated pooled VE as (1 minus the OR)×100 using a one-stage model with study site as a fixed effect. If the I(2) was >49% we used a two-stage random effects model.

RESULTS

We included in the A(H1N1)pdm09 analysis 531 cases and 1712 controls and in the A(H3N2) analysis 623 cases and 1920 controls. For A(H1N1)pdm09, the Q test (p=0.695) and the I(2) index (0%) suggested no heterogeneity of adjusted VE between study sites. Using a one-stage model, the overall pooled adjusted VE against influenza A(H1N1)pdm2009 was 47.5% (95% CI: 16.4-67.0). For A(H3N2), the I(2) was 51.5% (p=0.067). Using a two-stage model for the pooled analysis, the adjusted VE against A(H3N2) was 29.7 (95% CI: -34.4-63.2).

CONCLUSIONS

The results suggest a moderate 2013-2014 influenza VE against A(H1N1)pdm09 and a low VE against A(H3N2). The A(H3N2) estimates were heterogeneous among study sites. Larger sample sizes by study site are needed to prevent statistical heterogeneity, decrease variability and allow for two-stage pooled VE for all subgroup analyses.