Bias in control selection associated with the use of rapid tests in influenza vaccine effectiveness studies.

In test-negative design studies that use rapid tests to estimate influenza vaccine effectiveness (VE) a common concern is case/control misclassification due to imperfect test sensitivity and specificity. However, an imperfect test can also fail to exclude from the control group people that do not represent the source population, including people infected with other influenza types or other vaccine-preventable respiratory viruses for which vaccination status is correlated. We investigated these biases by comparing the effectiveness of seasonal 2023/24 influenza vaccination against influenza A and B based on PCR versus rapid test results, excluding controls who tested positive for SARS-CoV-2 or the other type of influenza.

Meeting Report From "Correlates of Protection for Next Generation Influenza Vaccines: Lessons Learned From the COVID-19 Pandemic".

Background: This report summarizes the discussions and conclusions from the "Correlates of Protection for Next Generation Influenza Vaccines: Lessons Learned from the COVID-19 Pandemic" meeting, which took place in Seattle, USA, from March 1, 2023, to March 3, 2023.

Conclusions: Discussions around influenza virus correlates of protection and their use continued from where the discussion had been left off in 2019. While there was not much progress in the influenza field itself, many lessons learned during the coronavirus disease 2019 (COVID-19) pandemic, especially the importance of mucosal immunity, were discussed and can directly be applied to influenza correlates of protection.

Hospitalizations and emergency attendance averted by influenza vaccination in Victoria, Australia, 2017 - 2019.

Seasonal influenza epidemics result in high levels of healthcare utilization. Vaccination is an effective strategy to reduce the influenza-related burden of disease. However, reporting vaccine effectiveness does not convey the population impacts of influenza vaccination.

Evaluating the impact of extended dosing intervals on mRNA COVID-19 vaccine effectiveness in adolescents.

Background: Extending the dosing interval of a primary series of mRNA COVID-19 vaccination has been employed to reduce myocarditis risk in adolescents, but previous evaluation of impact on vaccine effectiveness (VE) is limited to risk after second dose.

Methods: We quantified the impact of the dosing interval based on case notifications and vaccination uptake in Hong Kong from January to April 2022, based on calendar-time proportional hazards models and matching approaches.

Results: We estimated that the hazard ratio (HR) and odds ratio (OR) of infections after the second dose for extended (28 days or more) versus regular (21-27 days) dosing intervals ranged from 0.

Maternal influenza vaccination and associated risk of fetal loss: A claims-based prospective cohort study.

Background: Although numerous studies support the safety of influenza vaccination during pregnancy, fewer studies have evaluated the risk of miscarriage or considered the effect of prior immunization.

Methods: Using national de-identified administrative claims data from the Optum Labs Data Warehouse, we conducted a claims-based cohort study of 117,626 pregnancies between January 2009 and December 2018. We identified pandemic A(H1N1)pdm09 and seasonal influenza vaccinations using CPT codes.

Hemagglutination Inhibition Antibody Titers as Mediators of Influenza Vaccine Efficacy Against Symptomatic Influenza A(H1N1), A(H3N2), and B/Victoria Virus Infections.

Background: The hemagglutination inhibition antibody (HAI) titer contributes only a part of vaccine-induced protection against influenza virus infections. Using causal mediation analysis, we quantified the proportion of vaccine efficacy mediated by postvaccination HAI titers.

Methods: We conducted causal mediation analyses using data from a randomized, active-comparator controlled, phase III, trial of an inactivated, split-virion seasonal quadrivalent influenza vaccine in children conducted from October 2010 to December 2011 in 8 countries.

The Potential Benefits of Delaying Seasonal Influenza Vaccine Selections for the Northern Hemisphere: A Retrospective Modeling Study in the United States.

Background: Antigenic similarity between vaccine viruses and circulating viruses is crucial for achieving high vaccine effectiveness against seasonal influenza. New non-egg-based vaccine production technologies could revise current vaccine formulation schedules. We aim to assess the potential benefit of delaying seasonal influenza vaccine virus selection decisions.

An observational study on imported COVID-19 cases in Hong Kong during mandatory on-arrival hotel quarantine.

Background: Hong Kong enforced stringent travel restrictions during the COVID-19 pandemic. Understanding the characteristics of imported COVID-19 cases is important for establishing evidence-based control measures.

Methods: Retrospective cohort study summarising the characteristics of imported cases detected in Hong Kong between 13 November 2020 and 31 January 2022, when compulsory quarantine was implemented.

Memory B cell proliferation drives differences in neutralising responses between ChAdOx1 and BNT162b2 SARS-CoV-2 vaccines.

Vaccination against COVID-19 has been pivotal in reducing the global burden of the disease. However, Phase III trial results and observational studies underscore differences in efficacy across vaccine technologies and dosing regimens. Notably, mRNA vaccines have exhibited superior effectiveness compared to Adenovirus (AdV) vaccines, especially with extended dosing intervals.

Evaluating the impact of extended dosing intervals on mRNA COVID-19 vaccine effectiveness in adolescents.

Extending the dosing interval of a primary series of mRNA COVID-19 vaccination has been employed to reduce myocarditis risk in adolescents, but previous evaluation of impact on vaccine effectiveness (VE) is limited to risk after second dose. Here, we quantified the impact of the dosing interval based on case notifications and vaccination uptake in Hong Kong from January to April 2022. We estimated that the hazard ratio (HR) and odds ratio (OR) of infections after the second dose for extended (28 days or more) versus regular (21-27 days) dosing intervals ranged from 0.

Prior infections and effectiveness of SARS-CoV-2 vaccine in test-negative studies: a systematic review and meta-analysis.

Prior infection with SARS-CoV-2 can provide protection against infection and severe COVID-19. We aimed to determine the impact of preexisting immunity on vaccine effectiveness (VE) estimates. We systematically reviewed and meta-analyzed 66 test-negative design studies that examined VE against infection or severe disease (hospitalization, intensive care unit admission, or death) for primary vaccination series.

Relative Vaccine Effectiveness of Cell- vs Egg-Based Quadrivalent Influenza Vaccine Against Test-Confirmed Influenza Over 3 Seasons Between 2017 and 2020 in the United States.

Background: Influenza vaccine viruses grown in eggs may acquire egg-adaptive mutations that may reduce antigenic similarity between vaccine and circulating influenza viruses and decrease vaccine effectiveness. We compared cell- and egg-based quadrivalent influenza vaccines (QIVc and QIVe, respectively) for preventing test-confirmed influenza over 3 US influenza seasons (2017-2020).

Methods: Using a retrospective test-negative design, we estimated the relative vaccine effectiveness (rVE) of QIVc vs QIVe among individuals aged 4 to 64 years who had an acute respiratory or febrile illness and were tested for influenza in routine outpatient care.

Influenza vaccine effectiveness against hospitalizations associated with influenza A(H3N2) in Hong Kong children aged 9 months to 17 years, June-November 2023.

A test negative study was carried out from 13 June through to 15 November 2023 enrolling 3183 children hospitalized with acute respiratory illness in Hong Kong. Influenza A and B viruses were detected in 528 (16.6%) children, among which 419 (79.

Quantifying the impact of pre-vaccination titre and vaccination history on influenza vaccine immunogenicity.

Epidemiological studies suggest that heterogeneity in influenza vaccine antibody response is associated with host factors, including pre-vaccination immune status, age, gender, and vaccination history. However, the pattern of reported associations varies between studies. To better understand the underlying influences on antibody responses, we combined host factors and vaccine-induced in-host antibody kinetics from a cohort study conducted across multiple seasons with a unified analysis framework.

Risk of Severe Maternal Morbidity Associated With Severe Acute Respiratory Syndrome Coronavirus 2 Infection During Pregnancy.

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during pregnancy increases the risk of adverse fetal and neonatal outcomes, but the contribution to severe maternal morbidity (SMM) has been less frequently documented.

Methods: We conducted a national cohort study of 93 624 deliveries occurring between 11 March 2020 and 1 July 2021 using medical claims information from the OptumLabs Data Warehouse. SARS-CoV-2 infection was identified from diagnostic and laboratory testing claims records.

The relative effectiveness of three and four doses of COVID-19 vaccine in Victoria, Australia: A data linkage study.

Background: The Coronavirus Disease 2019 (COVID-19) pandemic led to extensive vaccination campaigns worldwide, including in Australia. Immunity waning and the emergence of new viral variants pose challenges to the effectiveness of vaccines. Our study aimed to assess the relative effectiveness (rVE) of 3 and 4 compared with 2 doses of COVID-19 vaccine.

Circulation of influenza and other respiratory viruses during the COVID-19 pandemic in Australia and New Zealand, 2020-2021.

Objective: Circulation patterns of influenza and other respiratory viruses have been globally disrupted since the emergence of coronavirus disease (COVID-19) and the introduction of public health and social measures (PHSMs) aimed at reducing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission.

Methods: We reviewed respiratory virus laboratory data, Google mobility data and PHSMs in five geographically diverse regions in Australia and New Zealand. We also described respiratory virus activity from January 2017 to August 2021.

Antigenic drift and subtype interference shape A(H3N2) epidemic dynamics in the United States.

Influenza viruses continually evolve new antigenic variants, through mutations in epitopes of their major surface proteins, hemagglutinin (HA) and neuraminidase (NA). Antigenic drift potentiates the reinfection of previously infected individuals, but the contribution of this process to variability in annual epidemics is not well understood. Here we link influenza A(H3N2) virus evolution to regional epidemic dynamics in the United States during 1997-2019.