End of season influenza vaccine effectiveness in adults and children in the United Kingdom in 2017/18

Real-world effectiveness of influenza vaccination in preventing influenza and influenza-like illness in children

BACKGROUND AND OBJECTIVES

Quadrivalent live attenuated influenza vaccines (LAIV-4) offer an alternative to inactivated influenza vaccines (IIV) for children aged 2-17 years, but data on their comparative effectiveness are limited. This study assessed vaccination rates and real-world effectiveness of LAIV-4 and IIV in preventing influenza and influenza-like illness (ILI) in Italian children during the 2022-2023 and 2023-2024 seasons.

METHODS

We conducted a population-based cohort study of children aged 2-14 years from September 2022 to April 2024, using data from Pedianet, a pediatric primary care database of anonymized records from family pediatricians. Children vaccinated with LAIV-4 or IIV were compared to unvaccinated children. The primary outcome was any first influenza or ILI episode. Monthly vaccination incidence rates per 1000 person-months were calculated for each vaccine type. Hazard ratios (HRs) and their 95 % confidence intervals (CIs) for vaccine effectiveness (VE) were estimated using adjusted mixed-effects Cox models.

RESULTS

A total of 65,545 (472,173 person-months) and 72,377 (527,348 person-months) children were included for the 2022-2023 and 2023-2024 seasons, respectively. Vaccination rates were 12.71 and 12.85 per 1000 person-months, respectively. Compared to unvaccinated children, LAIV-4 had an overall effectiveness of 43 % (95 % CI, 32 %-53 %), while IIV effectiveness was 54 % (95 % CI, 46 %-61 %). In 2022-2023, LAIV-4 (38 % [95 % CI, 12 %-56 %]) and IIV (49 % [95 % CI, 37 %-58 %]) had comparable effectiveness. In 2023-2024, LAIV-4 (40 % [95 % CI, 25 %-52 %]) was slightly less effective than IIV (58 % [95 % CI, 44 %-68 %])(p = 0.048).

CONCLUSIONS

An overall moderate, comparable effectiveness of LAIV-4 and IIV in preventing influenza/ILI among Italian children was observed.

An Optimised Live Attenuated Influenza Vaccine Ferret Efficacy Model Successfully Translates H1N1 Clinical Data

Between 2013 and 2016, the A/H1N1pdm09 component of the live attenuated influenza vaccine (LAIV) produced instances of lower-than-expected vaccine effectiveness. Standard pre-clinical ferret models, using a human-like vaccine dose and focusing on antigenic match to circulating wildtype (wt) strains, were unable to predict these fluctuations. By optimising the vaccine dose and utilising clinically relevant endpoints, we aimed to develop a ferret efficacy model able to reproduce clinical observations. Ferrets were intranasally vaccinated with 4 Log10 FFU/animal (1000-fold reduction compared to clinical dose) of seven historical LAIV formulations with known (19-90%) H1N1 vaccine efficacy or effectiveness (VE). Following homologous H1N1 wt virus challenge, protection was assessed based on primary endpoints of wt virus shedding in the upper respiratory tract and the development of fever. LAIV formulations with high (82-90%) H1N1 VE provided significant protection from wt challenge, while formulations with reduced (19-32%) VE tended not to provide significant protection. The strongest correlation observed was between reduction in wt shedding and VE (R2 = 0.75). Conversely, serum immunogenicity following vaccination was not a reliable indicator of protection (R2 = 0.37). This demonstrated that, by optimisation of the vaccine dose and the use of non-serological, clinically relevant protection endpoints, the ferret model could successfully translate clinical H1N1 LAIV VE data.

Influenza vaccination during the 2021/22 season: A data-linkage test-negative case-control study of effectiveness against influenza requiring emergency care in England and serological analysis of primary care patients

We present England 2021/22 end-of-season adjusted vaccine effectiveness (aVE) against laboratory confirmed influenza related emergency care use in children aged 1-17 and in adults aged 50+, and serological findings in vaccinated vs unvaccinated adults by hemagglutination inhibition assay. Influenza vaccination has been routinely offered to all children aged 2-10 years and adults aged 65 years + in England. In 2021/22, the offer was extended to children to age 15 years, and adults aged 50-64 years. Influenza activity rose during the latter half of the 2021/22 season, while remaining comparatively low due to COVID-19 pandemic control measures. Influenza A(H3N2) strains predominated. A test negative design was used to estimate aVE by vaccine type. Cases and controls were identified within a sentinel laboratory surveillance system. Vaccine histories were obtained from the National Immunisation Management Service (NIMS), an influenza and COVID-19 vaccine registry. These were linked to emergency department presentations (excluding accidents) with respiratory swabbing ≤ 14 days before or ≤ 7 days after presentation. Amongst adults, 423 positive and 32,917 negative samples were eligible for inclusion, and 145 positive and 6,438 negative samples among children. Those admitted to hospital were further identified. In serology against the circulating A(H3N2) A/Bangladesh/4005/2020-like strain, 61 % of current season adult vaccinees had titres ≥ 1:40 compared to 17 % of those unvaccinated in 2020/21 or 2021/22 (p < 0.001). We found good protection from influenza vaccination against influenza requiring emergency care in children (72.7 % [95 % CI 52.7, 84.3 %]) and modest effectiveness in adults (26.1 % [95 % CI 4.5, 42.8 %]). Adult VE was higher for A(H1N1) (81 % [95 % CI 50, 93 %]) than A(H3N2) (33 % [95 % CI 6, 53 %]). Consistent protection was observable across preschool, primary and secondary school aged children. Imperfect test specificity combined with very low prevalence may have biased estimates towards null. With limited influenza circulation, the study could not determine differences by vaccine types.

Effectiveness of the quadrivalent live attenuated influenza vaccine against influenza-related hospitalisations and morbidity among children aged 2 to 6 years in Denmark: a nationwide cohort study emulating a target trial

BACKGROUND

Scant evidence exists on the real-world effectiveness of quadrivalent live attenuated influenza vaccines (LAIV-4) in younger children. We aimed to assess the real-world effectiveness of LAIV-4 against influenza-related hospital contacts and admission and morbidity.

METHODS

Using nationwide Danish health-care registries, we designed a cohort study that emulates a target trial, comparing LAIV-4 to no vaccination in children aged 2-6 years. Eligible children vaccinated from Oct 1, 2021, to Jan 15, 2022, were matched to unvaccinated controls in a 1:1 ratio according to demographic characteristics and risk groups for influenza, and followed-up until May 31, 2022. Primary study outcomes any hospital contact for influenza and influenza-related hospital admissions more than 12 h in duration, while hospital admission for respiratory tract infections, or for wheezing or asthma, and antibiotic prescriptions were evaluated as secondary outcomes. We estimated incidence rate ratios (IRRs) and 95% CIs using Poisson regression for each outcome. Vaccine effectiveness was calculated as 1 - IRR.

FINDINGS

Among 308 520 Danish children aged 2-6 years, 95 434 vaccinated children were matched with 95 434 unvaccinated children who acted as controls. Receipt of LAIV-4 compared with no vaccination was associated with a reduced IRR of 0·36 (95% CI 0·27 to 0·46) and estimated vaccine effectiveness of 64·3% (53·6 to 72·6) against influenza-related hospital contacts (76 vs 210 events). The corresponding IRR and vaccine effectiveness against influenza-related hospital admissions were 0·63 (0·38 to 1·05) and 36·9% (-5·2 to 62·1; 24 vs 38 events), respectively. LAIV-4 was not associated with reductions in admission rates for respiratory tract infections (IRR 1·14, 95% CI 0·94 to 1·38), wheezing or asthma (1·04, 0·83 to 1·31), or antibiotic prescriptions for respiratory tract infections (0·97, 0·93 to 1·00). Vaccine effectiveness assessed across risk groups for influenza showed similar effectiveness in children with and without coexisting risk factors for severe influenza.

INTERPRETATION

LAIV-4 offered moderate protection in younger children against influenza-related hospital contacts during a season dominated by influenza A(H3N2); however vaccination was not associated with reductions in secondary outcomes. This real-world study thereby supports trial evidence of moderate vaccine effectiveness of LAIV-4 against influenza-related outcomes when implementing broad vaccination schedules in younger children.

FUNDING

Beckett-Fonden.

Influenza vaccination is associated with a reduced risk of invasive aspergillosis in high-risk individuals in Taiwan: a population-based cohort study

Invasive aspergillosis (IA) has become the emerging life-threatening disease in recent years. Influenza has been identified as an independent risk factor for IA. Vaccination is the most effective way to prevent influenza, while whether it can reduce IA in high-risk population still uncertain. We aimed to investigate the association between influenza vaccination and the risk of IA in high-risk population. We performed a population-based cohort study of people who qualified for government-funded influenza vaccination and were at high risk for IA at the start of the influenza season each year between 2016 and 2019. We utilized Taiwan's National Health Insurance Research Database to identify the influenza vaccination status and IA diagnosis during the follow-up period. We compared the risk of IA between people with and without vaccination using multivariable logistic regression analysis. Out of total 8,544,451 people who were eligible during the 3 influenza seasons, 3,136,477 (36.7%) were vaccinated. A total of 1179 IA cases with the incidence of 13.8 cases per 100,000 high-risk individuals were identified during the follow-up. Compared to non-vaccinated group, vaccinated individuals had a 21% risk reduction of IA (adjusted odds ratio 0.79, 95% confidence interval 0.70-0.90). Influenza vaccination was associated with a lower risk of IA among males, immunosuppressive conditions, malignancy, diabetes, and those having host factors according to the European Organization for Research and Treatment of Cancer and the Mycoses Study Group Education and Research Consortium. Influenza vaccination is recommended for high-risk population to reduce the risk of IA.

Assessing the value of integrating national longitudinal shopping data into respiratory disease forecasting models

The COVID-19 pandemic led to unparalleled pressure on healthcare services. Improved healthcare planning in relation to diseases affecting the respiratory system has consequently become a key concern. We investigated the value of integrating sales of non-prescription medications commonly bought for managing respiratory symptoms, to improve forecasting of weekly registered deaths from respiratory disease at local levels across England, by using over 2 billion transactions logged by a UK high street retailer from March 2016 to March 2020. We report the results from the novel AI (Artificial Intelligence) explainability variable importance tool Model Class Reliance implemented on the PADRUS model (Prediction of Amount of Deaths by Respiratory disease Using Sales). PADRUS is a machine learning model optimised to predict registered deaths from respiratory disease in 314 local authority areas across England through the integration of shopping sales data and focused on purchases of non-prescription medications. We found strong evidence that models incorporating sales data significantly out-perform other models that solely use variables traditionally associated with respiratory disease (e.g. sociodemographics and weather data). Accuracy gains are highest (increases in R2 (coefficient of determination) between 0.09 to 0.11) in periods of maximum risk to the general public. Results demonstrate the potential to utilise sales data to monitor population health with information at a high level of geographic granularity.

The interplay between susceptibility and vaccine effectiveness control the timing and size of an emerging seasonal influenza wave in England

Relaxing social distancing measures and reduced level of influenza over the last two seasons may lead to a winter 2022 influenza wave in England. We used an established model for influenza transmission and vaccination to evaluate the rolled out influenza immunisation programme over October to December 2022. Specifically, we explored how the interplay between pre-season population susceptibility and influenza vaccine efficacy control the timing and the size of a possible winter influenza wave. Our findings suggest that susceptibility affects the timing and the height of a potential influenza wave, with higher susceptibility leading to an earlier and larger influenza wave while vaccine efficacy controls the size of the peak of the influenza wave. With pre-season susceptibility higher than pre-COVID-19 levels, under the planned vaccine programme an early influenza epidemic wave is possible, its size dependent on vaccine effectiveness against the circulating strain. If pre-season susceptibility is low and similar to pre-COVID levels, the planned influenza vaccine programme with an effective vaccine could largely suppress a winter 2022 influenza outbreak in England.

Seasonal Influenza Vaccine Effectiveness in Persons Aged 15-64 Years: A Systematic Review and Meta-Analysis

Influenza is a respiratory disease caused by the influenza virus, which is highly transmissible in humans. This paper presents a systematic review and meta-analysis of randomized controlled trials (RCTs) and test-negative designs (TNDs) to assess the vaccine effectiveness (VE) of seasonal influenza vaccines (SIVs) in humans aged 15 to 64 years. An electronic search to identify all relevant studies was performed. The outcome measure of interest was VE on laboratory-confirmed influenza (any strain). Quality assessment was performed using the Cochrane risk-of-bias tool for RCTs and the ROBINS-I tool for TNDs. The search identified a total of 2993 records, but only 123 studies from 73 papers were included in the meta-analysis. Of these studies, 9 were RCTs and 116 were TNDs. The pooled VE was 48% (95% CI: 42-54) for RCTs, 55.4% (95% CI: 43.2-64.9) when there was a match between the vaccine and most prevalent circulating strains and 39.3% (95% CI: 23.5-51.9) otherwise. The TNDs' adjusted VE was equal to 39.9% (95% CI: 31-48), 45.1 (95% CI: 38.7-50.8) when there was a match and 35.1 (95% CI: 29.0-40.7) otherwise. The match between strains included in the vaccine and strains in circulation is the most important factor in the VE. It increases by more than 25% when there is a match with the most prevalent circulating strains. The laboratorial method for confirmation of influenza is a possible source of bias when estimating VE.

Efficacy and effectiveness of influenza vaccination in healthy children. A review of current evidence

Influenza is common in healthy children and adolescents and is associated with a high rate of hospitalization in this group, especially for those <5 years. Although the WHO has recommended vaccination in children under 5 years of age since 2012, it is really implemented in few countries today. The aim of this paper was to review the available evidence on the efficacy/effectiveness of influenza vaccination in healthy children <18 years of age through a non-systematic search of studies conducted between 2010 and 2020. Despite the high variability in results due to differences in design, vaccine type and season included in the 41 selected studies, statistically significant studies show efficacy values for the influenza vaccine of between 25.6% and 74.2%, and effectiveness from 26% to 78.8%. Although a systematic review would be necessary to corroborate the evidence, this review suggests that paediatric vaccination is generally an effective measure for preventing influenza in healthy children in line with international organisms' recommendations.

Impact of General Practitioner Education on Acceptance of an Adjuvanted Seasonal Influenza Vaccine among Older Adults in England

Seasonal vaccination against influenza and in-pandemic COVID-19 vaccination are top public health priorities; vaccines are the primary means of reducing infections and also controlling pressures on health systems. During the 2018-2019 influenza season, we conducted a study of the knowledge, attitudes, and behaviours of 159 general practitioners (GPs) and 189 patients aged ≥65 years in England using a combination of qualitative and quantitative approaches to document beliefs about seasonal influenza and seasonal influenza vaccine. GPs were surveyed before and after a continuing medical education (CME) module on influenza disease and vaccination with an adjuvanted trivalent influenza vaccine (aTIV) designed for patients aged ≥65 years, and patients were surveyed before and after a routine visit with a GP who participated in the CME portion of the study. The CME course was associated with significantly increased GP confidence in their ability to address patients' questions and concerns about influenza disease and vaccination (p < 0.001). Patients reported significantly increased confidence in the effectiveness and safety of aTIV after meeting their GP. Overall, 82.2% of the study population were vaccinated against influenza (including 137 patients vaccinated during the GP visit and 15 patients who had been previously vaccinated), a rate higher than the English national average vaccine uptake of 72.0% that season. These findings support the value of GP-patient interactions to foster vaccine acceptance.

Does repeated influenza vaccination attenuate effectiveness? A systematic review and meta-analysis

BACKGROUND

Influenza vaccines require annual readministration; however, several reports have suggested that repeated vaccination might attenuate the vaccine's effectiveness. We aimed to estimate the reduction in vaccine effectiveness associated with repeated influenza vaccination.

METHODS

In this systematic review and meta-analysis, we searched MEDLINE, EMBASE, and CINAHL Complete databases for articles published from Jan 1, 2016, to June 13, 2022, and Web of Science for studies published from database inception to June 13, 2022. For studies published before Jan 1, 2016, we consulted published systematic reviews. Two reviewers (EJ-G and EJR) independently screened, extracted data using a data collection form, assessed studies' risk of bias using the Risk Of Bias In Non-Randomized Studies of Interventions (ROBINS-I) and evaluated the weight of evidence by Grading of Recommendations Assessment, Development, and Evaluation (GRADE). We included observational studies and randomised controlled trials that reported vaccine effectiveness against influenza A(H1N1)pdm09, influenza A(H3N2), or influenza B using four vaccination groups: current season; previous season; current and previous seasons; and neither season (reference). For each study, we calculated the absolute difference in vaccine effectiveness (ΔVE) for current season only and previous season only versus current and previous season vaccination to estimate attenuation associated with repeated vaccination. Pooled vaccine effectiveness and ∆VE were calculated by season, age group, and overall. This study is registered with PROSPERO, CRD42021260242.

FINDINGS

We identified 4979 publications, selected 681 for full review, and included 83 in the systematic review and 41 in meta-analyses. ΔVE for vaccination in both seasons compared with the current season was -9% (95% CI -16 to -1, I2=0%; low certainty) for influenza A(H1N1)pdm09, -18% (-26 to -11, I2=7%; low certainty) for influenza A(H3N2), and -7% (-14 to 0, I2=0%; low certainty) for influenza B, indicating lower protection with consecutive vaccination. However, for all types, A subtypes and B lineages, vaccination in both seasons afforded better protection than not being vaccinated.

INTERPRETATION

Our estimates suggest that, although vaccination in the previous year attenuates vaccine effectiveness, vaccination in two consecutive years provides better protection than does no vaccination. The estimated effects of vaccination in the previous year are concerning and warrant additional investigation, but are not consistent or severe enough to support an alternative vaccination regimen at this time.

FUNDING

WHO and the US National Institutes of Health.

How the COVID 19 pandemic will shape influenza public health initiatives: The UK experience

Although caused by different pathogens, COVID-19 and influenza share many clinical features, as well as the potential for inflammatory, cardiovascular, and other long-term complications. During the 2020-2021 influenza season, COVID-19 mitigation efforts and a robust influenza vaccination campaign led to an unprecedented reduction in influenza cases. The lack of exposure to influenza, along with antigenic changes, may have reduced population immunity to influenza and set the stage for a high severity influenza season in 2021-2022. For the second consecutive season, the UK Department of Health and Social Care has expanded influenza vaccine eligibility to mitigate the impact of both COVID-19 and influenza. Continuation of clear policy decisions, as well as ongoing coordination between manufacturers, distributors, health authorities, and healthcare providers, is key to reducing the burden of influenza and COVID-19 and preventing large numbers of severe cases that can overwhelm the healthcare system.

Strain development of A/H1N1pdm09 candidate vaccine viruses for the 2021–22 northern hemisphere influenza season

The vaccine effectiveness (VE) of the A/H1N1pdm09 component of the 2017–18 quadrivalent live attenuated influenza vaccine (QLAIV) was improved by performing rational haemagglutinin (HA) mutagenesis. Introducing N125D, D127E, D222G and R223Q substitutions into the HA protein of A/Slovenia/2903/2015 (A/SLOV15) enhanced replicative fitness in primary human nasal epithelial cells (hNECs). This allowed A/SLOV15 to overcome inter-strain competition in QLAIV, resulting in improved VE.

During strain development for the 2021–22 QLAIV formulation, A/H1N1pdm09 LAIV viruses containing wild-type (WT) HA and neuraminidase (NA) sequences were found to replicate poorly in embryonated eggs and hNECs. We aimed to enhance replicative fitness via the HA mutagenesis approach that was performed previously for A/SLOV15. Therefore, combinations of these four mutations were introduced into the HA protein of representative 6B.1A-5a.2 viruses, A/Victoria/2570/2019 and A/Victoria/1/2020 (A/VIC1). Replicative fitness of A/VIC1 V7 was improved ~30-fold in eggs and ~300-fold in hNECs relative to its parent, without compromising other critical LAIV characteristics.

Influenza Vaccine Effectiveness by A(H3N2) Phylogenetic Subcluster and Prior Vaccination History: 2016-2017 and 2017-2018 Epidemics in Canada

BACKGROUND

The influenza A(H3N2) vaccine was updated from clade 3C.3a in 2015-2016 to 3C.2a for 2016-2017 and 2017-2018. Circulating 3C.2a viruses showed considerable hemagglutinin glycoprotein diversification and the egg-adapted vaccine also bore mutations.

METHODS

Vaccine effectiveness (VE) in 2016-2017 and 2017-2018 was assessed by test-negative design, explored by A(H3N2) phylogenetic subcluster and prior season's vaccination history.

RESULTS

In 2016-2017, A(H3N2) VE was 36% (95% confidence interval [CI], 18%-50%), comparable with (43%; 95% CI, 24%-58%) or without (33%; 95% CI, -21% to 62%) prior season's vaccination. In 2017-2018, VE was 14% (95% CI, -8% to 31%), lower with (9%; 95% CI, -18% to 30%) versus without (45%; 95% CI, -7% to 71%) prior season's vaccination. In 2016-2017, VE against predominant clade 3C.2a1 viruses was 33% (95% CI, 11%-50%): 18% (95% CI, -40% to 52%) for 3C.2a1a defined by a pivotal T135K loss of glycosylation; 60% (95% CI, 19%-81%) for 3C.2a1b (without T135K); and 31% (95% CI, 2%-51%) for other 3C.2a1 variants (with/without T135K). VE against 3C.2a2 viruses was 45% (95% CI, 2%-70%) in 2016-2017 but 15% (95% CI, -7% to 33%) in 2017-2018 when 3C.2a2 predominated. VE against 3C.2a1b in 2017-2018 was 37% (95% CI, -57% to 75%), lower at 12% (95% CI, -129% to 67%) for a new 3C.2a1b subcluster (n = 28) also bearing T135K.

CONCLUSIONS

Exploring VE by phylogenetic subcluster and prior vaccination history reveals informative heterogeneity. Pivotal mutations affecting glycosylation sites, and repeat vaccination using unchanged antigen, may reduce VE.

Opposing Effects of Prior Infection versus Prior Vaccination on Vaccine Immunogenicity against Influenza A(H3N2) Viruses

Prior vaccination can alternately enhance or attenuate influenza vaccine immunogenicity and effectiveness. Analogously, we found that vaccine immunogenicity was enhanced by prior A(H3N2) virus infection among participants of the Ha Nam Cohort, Viet Nam, but was attenuated by prior vaccination among Australian Health Care Workers (HCWs) vaccinated in the same year. Here, we combined these studies to directly compare antibody titers against 35 A(H3N2) viruses spanning 1968-2018. Participants received licensed inactivated vaccines containing A/HongKong/4801/2014 (H3N2). The analysis was limited to participants aged 18-65 Y, and compared those exposed to A(H3N2) viruses circulating since 2009 by infection (Ha Nam) or vaccination (HCWs) to a reference group who had no recent A(H3N2) infection or vaccination (Ha Nam). Antibody responses were compared by fitting titer/titer-rise landscapes across strains, and by estimating titer ratios to the reference group of 2009-2018 viruses. Pre-vaccination, titers were lowest against 2009-2014 viruses among the reference (no recent exposure) group. Post-vaccination, titers were, on average, two-fold higher among participants with prior infection and two-fold lower among participants with 3-5 prior vaccinations compared to the reference group. Titer rise was negligible among participants with 3-5 prior vaccinations, poor among participants with 1-2 prior vaccinations, and equivalent or better among those with prior infection compared to the reference group. The enhancing effect of prior infection versus the incrementally attenuating effect of prior vaccinations suggests that these exposures may alternately promote and constrain the generation of memory that can be recalled by a new vaccine strain.

Investigating the uptake, effectiveness and safety of COVID-19 vaccines: protocol for an observational study using linked UK national data

INTRODUCTION

The novel coronavirus SARS-CoV-2, which emerged in December 2019, has caused millions of deaths and severe illness worldwide. Numerous vaccines are currently under development of which a few have now been authorised for population-level administration by several countries. As of 20 September 2021, over 48 million people have received their first vaccine dose and over 44 million people have received their second vaccine dose across the UK. We aim to assess the uptake rates, effectiveness, and safety of all currently approved COVID-19 vaccines in the UK.

METHODS AND ANALYSIS

We will use prospective cohort study designs to assess vaccine uptake, effectiveness and safety against clinical outcomes and deaths. Test-negative case-control study design will be used to assess vaccine effectiveness (VE) against laboratory confirmed SARS-CoV-2 infection. Self-controlled case series and retrospective cohort study designs will be carried out to assess vaccine safety against mild-to-moderate and severe adverse events, respectively. Individual-level pseudonymised data from primary care, secondary care, laboratory test and death records will be linked and analysed in secure research environments in each UK nation. Univariate and multivariate logistic regression models will be carried out to estimate vaccine uptake levels in relation to various population characteristics. VE estimates against laboratory confirmed SARS-CoV-2 infection will be generated using a generalised additive logistic model. Time-dependent Cox models will be used to estimate the VE against clinical outcomes and deaths. The safety of the vaccines will be assessed using logistic regression models with an offset for the length of the risk period. Where possible, data will be meta-analysed across the UK nations.

ETHICS AND DISSEMINATION

We obtained approvals from the National Research Ethics Service Committee, Southeast Scotland 02 (12/SS/0201), the Secure Anonymised Information Linkage independent Information Governance Review Panel project number 0911. Concerning English data, University of Oxford is compliant with the General Data Protection Regulation and the National Health Service (NHS) Digital Data Security and Protection Policy. This is an approved study (Integrated Research Application ID 301740, Health Research Authority (HRA) Research Ethics Committee 21/HRA/2786). The Oxford-Royal College of General Practitioners Clinical Informatics Digital Hub meets NHS Digital's Data Security and Protection Toolkit requirements. In Northern Ireland, the project was approved by the Honest Broker Governance Board, project number 0064. Findings will be made available to national policy-makers, presented at conferences and published in peer-reviewed journals.

Live Attenuated Cold-Adapted Influenza Vaccines

Live attenuated, cold-adapted influenza vaccines exhibit several desirable characteristics, including the induction of systemic, mucosal, and cell-mediated immunity resulting in breadth of protection, ease of administration, and yield. Seasonal live attenuated influenza vaccines (LAIVs) were developed in the United States and Russia and have been used in several countries. In the last decade, following the incorporation of the 2009 pandemic H1N1 strain, the performance of both LAIVs has been variable and the U.S.-backbone LAIV was less effective than the corresponding inactivated influenza vaccines. The cause appears to be reduced replicative fitness of some H1N1pdm09 viruses, indicating a need for careful selection of strains included in multivalent LAIV formulations. Assays are now being implemented to select optimal strains. An improved understanding of the determinants of replicative fitness of vaccine strains and of vaccine effectiveness of LAIVs is needed for public health systems to take full advantage of these valuable vaccines.

Interactions between SARS-CoV-2 and influenza, and the impact of coinfection on disease severity: a test-negative design

BACKGROUND

The impact of SARS-CoV-2 alongside influenza is a major concern in the northern hemisphere as winter approaches.

METHODS

Test data for influenza and SARS-CoV-2 from national surveillance systems between 20 January 2020 and 25 April 2020 were used to estimate influenza infection on the risk of SARS-CoV-2 infection. A test-negative design was used to assess the odds of SARS-CoV-2 in those who tested positive for influenza compared with those who tested negative. The severity of SARS-CoV-2 was also assessed using univariable and multivariable analyses.

RESULTS

The risk of testing positive for SARS-CoV-2 was 58% lower among influenza-positive cases and patients with a coinfection had a risk of death of 5.92 (95% confidence interval: 3.21-10.91) times greater than among those with neither influenza nor SARS-CoV-2. The odds of ventilator use or death and intensive care unit admission or death were greatest among coinfected patients.

CONCLUSIONS

Coinfection of these viruses could have a significant impact on morbidity, mortality and health-service demand.

Effectiveness of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines on covid-19 related symptoms, hospital admissions, and mortality in older adults in England: test negative case-control study

OBJECTIVE

To estimate the real world effectiveness of the Pfizer-BioNTech BNT162b2 and Oxford-AstraZeneca ChAdOx1-S vaccines against confirmed covid-19 symptoms (including the UK variant of concern B.1.1.7), admissions to hospital, and deaths.

DESIGN

Test negative case-control study.

SETTING

Community testing for covid-19 in England.

PARTICIPANTS

156 930 adults aged 70 years and older who reported symptoms of covid-19 between 8 December 2020 and 19 February 2021 and were successfully linked to vaccination data in the National Immunisation Management System.

INTERVENTIONS

Vaccination with BNT162b2 or ChAdOx1-S.

MAIN OUTCOME MEASURES

Primary outcomes were polymerase chain reaction confirmed symptomatic SARS-CoV-2 infections, admissions to hospital for covid-19, and deaths with covid-19.

RESULTS

Participants aged 80 years and older vaccinated with BNT162b2 before 4 January 2021 had a higher odds of testing positive for covid-19 in the first nine days after vaccination (odds ratio up to 1.48, 95% confidence interval 1.23 to 1.77), indicating that those initially targeted had a higher underlying risk of infection. Vaccine effectiveness was therefore compared with the baseline post-vaccination period. Vaccine effects were noted 10 to 13 days after vaccination, reaching a vaccine effectiveness of 70% (95% confidence interval 59% to 78%), then plateauing. From 14 days after the second dose a vaccination effectiveness of 89% (85% to 93%) was found compared with the increased baseline risk. Participants aged 70 years and older vaccinated from 4 January (when ChAdOx1-S delivery commenced) had a similar underlying risk of covid-19 to unvaccinated individuals. With BNT162b2, vaccine effectiveness reached 61% (51% to 69%) from 28 to 34 days after vaccination, then plateaued. With ChAdOx1-S, effects were seen from 14 to 20 days after vaccination, reaching an effectiveness of 60% (41% to 73%) from 28 to 34 days, increasing to 73% (27% to 90%) from day 35 onwards. On top of the protection against symptomatic disease, a further 43% (33% to 52%) reduced risk of emergency hospital admission and 51% (37% to 62%) reduced risk of death was observed in those who had received one dose of BNT162b2. Participants who had received one dose of ChAdOx1-S had a further 37% (3% to 59%) reduced risk of emergency hospital admission. Follow-up was insufficient to assess the effect of ChAdOx1-S on mortality. Combined with the effect against symptomatic disease, a single dose of either vaccine was about 80% effective at preventing admission to hospital with covid-19 and a single dose of BNT162b2 was 85% effective at preventing death with covid-19.

CONCLUSION

Vaccination with either one dose of BNT162b2 or ChAdOx1-S was associated with a significant reduction in symptomatic covid-19 in older adults, and with further protection against severe disease. Both vaccines showed similar effects. Protection was maintained for the duration of follow-up (>6 weeks). A second dose of BNT162b2 was associated with further protection against symptomatic disease. A clear effect of the vaccines against the B.1.1.7 variant was found.

Age-Specific Seasonal Influenza Vaccine Effectiveness against Different Influenza Subtypes in the Hospitalized Population in Lithuania during the 2015-2019 Influenza Seasons

Background: Continuous monitoring of seasonal influenza vaccine effectiveness (SIVE) is needed due to the changing nature of influenza viruses and it supports the decision on the annual update of vaccine composition. Age-specific SIVE was evaluated against different influenza subtypes in the hospitalized population in Lithuania during four influenza seasons. Methods: A test-negative case-control study design was used. SIVE and its 95% confidence intervals (95% CI) were calculated as (1 – odds ratio (OR)) × 100%. Results: Adjusted SIVE in 18–64-year-old individuals against influenza A, A(H1N1)pdm09 and B/Yamagata were 78.0% (95% CI: 1.7; 95.1%), 88.6% (95% CI: −47.4; 99.1%), and 76.8% (95% CI: −109.9; 97.4%), respectively. Adjusted SIVE in individuals aged 65 years and older against influenza A, influenza B, and B/Yamagata were 22.6% (95% CI: −36.5; 56.1%), 75.3% (95% CI: 12.2; 93.1%) and 73.1% (95% CI: 3.2; 92.5%), respectively. Unadjusted SIVE against influenza A(H3N2) among 18–64-year-old patients was 44.8% (95% CI: −171.0; 88.8%) and among those aged 65 years and older was 5.0% (95% CI: −74.5; 48.3%). Conclusions: Point estimates suggest high SIVE against influenza A in 18–64-year-old participants, and against influenza B and B/Yamagata in those 65 years old and older.

Pre-existing influenza-specific nasal IgA or nasal viral infection does not affect live attenuated influenza vaccine immunogenicity in children

The United Kingdom has a national immunization programme which includes annual influenza vaccination in school-aged children, using live attenuated influenza vaccine (LAIV). LAIV is given annually, and it is unclear whether repeat administration can affect immunogenicity. Because LAIV is delivered intranasally, pre-existing local antibody might be important. In this study, we analysed banked samples from a study performed during the 2017/18 influenza season to investigate the role of pre-existing influenza-specific nasal immunoglobulin (Ig)A in children aged 6-14 years. Nasopharyngeal swabs were collected prior to LAIV immunization to measure pre-existing IgA levels and test for concurrent upper respiratory tract viral infections (URTI). Oral fluid samples were taken at baseline and 21-28 days after LAIV to measure IgG as a surrogate of immunogenicity. Antibody levels at baseline were compared with a pre-existing data set of LAIV shedding from the same individuals, measured by reverse transcription-polymerase chain reaction. There was detectable nasal IgA specific to all four strains in the vaccine at baseline. However, baseline nasal IgA did not correlate with the fold change in IgG response to the vaccine. Baseline nasal IgA also did not have an impact upon whether vaccine virus RNA was detectable after immunization. There was no difference in fold change of antibody between individuals with and without an URTI at the time of immunization. Overall, we observed no effect of pre-existing influenza-specific nasal antibody levels on immunogenicity, supporting annual immunization with LAIV in children.

Decline in Seasonal Influenza Vaccine Effectiveness With Vaccination Program Maturation: A Systematic Review and Meta-analysis

BACKGROUND

Evidence suggests that repeated influenza vaccination may reduce vaccine effectiveness (VE). Using influenza vaccination program maturation (PM; number of years since program inception) as a proxy for population-level repeated vaccination, we assessed the impact on pooled adjusted end-season VE estimates from outpatient test-negative design studies.

METHODS

We systematically searched and selected full-text publications from January 2011 to February 2020 (PROSPERO: CRD42017064595). We obtained influenza vaccination program inception year for each country and calculated PM as the difference between the year of deployment and year of program inception. We categorized PM into halves (cut at the median), tertiles, and quartiles and calculated pooled VE using an inverse-variance random-effects model. The primary outcome was pooled VE against all influenza.

RESULTS

We included 72 articles from 11 931 citations. Across the 3 categorizations of PM, a lower pooled VE against all influenza for all patients was observed with PM. Substantially higher reductions were observed in older adults (≥65 years). We observed similar results for A(H1N1)pdm09, A(H3N2), and influenza B.

CONCLUSIONS

The evidence suggests that influenza VE declines with vaccination PM. This study forms the basis for further discussions and examinations of the potential impact of vaccination PM on seasonal VE.

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 Influenza Vaccine Administration and Primary Care Consultations for Respiratory Infections: Sentinel Network Study of Five Seasons (2014/2015-2018/2019) in the UK

Influenza, a vaccine preventable disease, is a serious global public health concern which results in a considerable burden on the healthcare system. However, vaccine hesitancy is increasingly becoming a global problem. One prevalent misconception is that influenza vaccinations can cause the flu. We carried out this study to determine whether people undertaking influenza vaccination presented less with acute respiratory tract infection (ARTI) and influenza-like-illness (ILI) following vaccination. We utilised the Oxford Royal College of General Practitioners Research and Surveillance Centre sentinel database to examine English patients who received vaccination between 2014/2015 and 2018/2019. Of the 3,841,700 influenza vaccinations identified, vaccination details and primary care respiratory consultation counts were extracted to calculate the relative incidence (RI) per exposure risk period using the self-controlled case series methodology. Results showed a significant increase in the RI of respiratory consultation rates within fourteen days of vaccination across all five years. Less than 6.2% of vaccinations led to consultations for ARTI or ILI in primary care (crude consultation rate 6196 per 100,000). These findings, particularly if confirmed in further research, may reduce the risk of cross-infection between waiting patients and increase uptake of influenza vaccine.

Optimising age coverage of seasonal influenza vaccination in England: A mathematical and health economic evaluation

For infectious disease prevention, policy-makers are typically required to base policy decisions in light of operational and monetary restrictions, prohibiting implementation of all candidate interventions. To inform the evidence-base underpinning policy decision making, mathematical and health economic modelling can be a valuable constituent.

Applied to England, this study aims to identify the optimal target age groups when extending a seasonal influenza vaccination programme of at-risk individuals to those individuals at low risk of developing complications following infection. To perform this analysis, we utilise an age- and strain-structured transmission model that includes immunity propagation mechanisms which link prior season epidemiological outcomes to immunity at the beginning of the following season. Making use of surveillance data from the past decade in conjunction with our dynamic model, we simulate transmission dynamics of seasonal influenza in England from 2012 to 2018. We infer that modified susceptibility due to natural infection in the previous influenza season is the only immunity propagation mechanism to deliver a non-negligible impact on the transmission dynamics. Further, we discerned case ascertainment to be higher for young infants compared to adults under 65 years old, and uncovered a decrease in case ascertainment as age increased from 65 to 85 years of age.

Our health economic appraisal sweeps vaccination age space to determine threshold vaccine dose prices achieving cost-effectiveness under differing paired strategies. In particular, we model offering vaccination to all those low-risk individuals younger than a given age (but no younger than two years old) and all low-risk individuals older than a given age, while maintaining vaccination of at-risk individuals of any age. All posited strategies were deemed cost-effective. In general, the addition of low-risk vaccination programmes whose coverage encompassed children and young adults (aged 20 and below) were highly cost-effective. The inclusion of elder age-groups to the low-risk programme typically lessened the cost-effectiveness. Notably, elderly-centric programmes vaccinating from 65-75 years and above had the least permitted expense per vaccine.

Vaccination is an established method to provide protection against seasonal influenza and its complications. Yet, a need to administer an updated vaccine on an annual basis presents significant operational challenges and sizeable costs. Consequently, policy makers typically have to decide how to deploy a finite amount of resource in a cost-effective manner. A combination of mathematical and health economic modelling can be used to address such a question. Here, we developed an age- and strain-structured mathematical model for seasonal influenza transmission dynamics that incorporates mechanisms for immunity propagation, which we used to reconstruct transmission dynamics of seasonal influenza in England from 2012 to 2018.

We then performed a health economic evaluation assessing the cost-effectiveness of extending a seasonal influenza vaccination programme of at-risk individuals to also include, for targeted age groups, those individuals at low risk of developing complications following infection. The findings suggest the inclusion of low-risk vaccination programmes whose coverage encompassed children and young adults (aged 20 and below) to be highly cost-effective. In contrast, the inclusion of elder age-groups to the low-risk programme typically lessened the cost-effectiveness.

La gripe: 76 años de vacuna antigripal… ¡y de la hemaglutinina!

Se revisa someramente la historia de los virus gripales y los pasos dados desde que se utilizó masivamente la primera vacuna de virus completos, hasta la descripción de las distintas vías de vehiculizar o de administrar la hemaglutinina de las que disponemos en la actualidad, en aras de mejorar la respuesta inmune y por tanto la protección clínica de toda la población. Se exponen brevemente los requisitos que debería cumplir una futura vacuna “universal” para que pudiera ser usada con carácter sistemático y los distintos proyectos en marcha.

Heterogeneity of Circulating Influenza Viruses and Their Impact on Influenza Virus Vaccine Effectiveness During the Influenza Seasons 2016/17 to 2018/19 in Austria

The constantly changing pattern in the dominance of viral strains and their evolving subclades during the seasons substantially influences influenza vaccine effectiveness (IVE). In order to further substantiate the importance of detailed data of genetic virus characterization for IVE estimates during the seasons, we performed influenza virus type and subtype specific IVE estimates. IVE estimates were assessed using a test-negative case-control design, in the context of the intraseasonal changes of the heterogeneous mix of circulating influenza virus strains for three influenza seasons (2016/17 to 2018/19) in Austria. Adjusted overall IVE over the three seasons 2016/17, 2017/18, and 2018/19 were -26, 39, and 63%, respectively. In accordance with the changing pattern of the circulating strains a broad range of overall and subtype specific IVEs was obtained: A(H3N2) specific IVE ranged between -26% for season 2016/17 to 58% in season 2018/19, A(H1N1)pdm09 specific IVE was 25% for the season 2017/18 and 65% for the season 2018/19 and Influenza B specific IVE for season 2017/18 was 45%. The results obtained in our study over the three seasons demonstrate the increasingly complex dynamic of the ever changing genetic pattern of the circulating influenza viruses and their influence on IVE estimates. This emphasizes the importance of detailed genetic virus surveillance for reliable IVE estimates.

Insights into current clinical research on the immunogenicity of live attenuated influenza vaccines

Introduction: Live attenuated influenza vaccines (LAIVs) have been in use for more than three decades and are now licensed in many countries. There is evidence that LAIVs can have greater efficacy than inactivated influenza vaccines, especially against mismatched influenza, however, in recent years, a number of trials have found a lack of LAIV efficacy, mainly in relation to the H1N1 virus.Areas covered: In this review, we summarize the results of clinical research published in the past 5 years on the immunogenicity of LAIVs, with special attention to the mechanisms of establishing protective immunity and some factors that may influence immunogenicity and efficacy.Expert opinion: A number of recent clinical studies confirmed that the immune responses to LAIVs are multifaceted, involving different immune mechanisms. These trials suggest that the intrinsic replicative properties of each LAIV component should be taken into account, and the precise effects of adding a fourth vaccine strain to trivalent LAIV formulations are still to be identified. In addition, new data are emerging regarding the impact of pre-vaccination conditions, such as preexisting immunity or concurrent asymptomatic viral and bacterial respiratory infections, on LAIV immunogenicity, suggesting the importance of monitoring them during clinical trials or vaccination campaigns.