Faculty Opinions recommendation of Estimation of influenza vaccine effectiveness from routine surveillance data.

Background. In Switzerland, SARS-CoV-2 vaccination campaigns started early 2021. Vaccine coverage reached 65% of the population in December 2021, mostly using mRNA vaccines from Moderna and Pfizer-BioNtech. Simultaneously, the proportion of vaccinated among COVID-19-related hospitalizations and deaths rose, creating some confusion in the general population. We aim to assess vaccine effectiveness against severe forms of SARS-CoV-2 infection using routine surveillance data on the vaccination status of COVID-19-related hospitalizations and deaths and data on vaccination coverage in Switzerland.Methods. We consider all routine surveillance data on COVID-19-related hospitalizations and deaths received at the Swiss Federal Office of Public Health from 1 July 2021 to 1 December 2021. We estimate the relative risk of COVID-19 related hospitalization or death for non-fully vaccinated compared to fully vaccinated individuals, adjusted for the dynamics of vaccination coverage over time, by age and location. We stratify the analysis by age group and by calendar month. We assess variations in the relative risk of hospitalization associated with the time since vaccination.Results. We include a total of 5,948 COVID-19-related hospitalizations of which 1,245 (21%) were fully vaccinated, and a total of 739 deaths of which 259 (35%) were fully vaccinated. We find that the relative risk of COVID-19 related hospitalization is 12.5 (95%CI: 11.7 to 13.4) times higher for non-fully vaccinated than for fully vaccinated individuals. This translates into a vaccine effectiveness against hospitalization of 92.0% (95%CI: 91.4 to 92.5%). Vaccine effectiveness against death is estimated to 90.3% (95%CI: 88.6 to 91.8%). Effectiveness appears comparatively lower in age groups over 70 and during the months of October and November 2021. We also find evidence of a decrease in vaccine effectiveness against hospitalization for individuals vaccinated for 25 weeks or more, but this decrease only appears in age groups below 70.Conclusions. The observed proportions of vaccinated among COVD-19-related hospitalizations and deaths in Switzerland are compatible with a high effectiveness of mRNA vaccines from Moderna and Pfizer-BioNtech against hospitalization and death in all age groups. Effectiveness appears comparatively lower in older age groups, suggesting the importance of booster vaccinations. We find inconclusive evidence that vaccine effectiveness is waning over time. Repeated analyses will be able to better assess waning and the effect of boosters.

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Differences between Frequentist and Bayesian inference in routine surveillance for influenza vaccine effectiveness: a test-negative case-control study

BMC Public Health ◽

10.1186/s12889-021-10543-z ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Michael L. Jackson ◽

Jill Ferdinands ◽

Mary Patricia Nowalk ◽

Richard K. Zimmerman ◽

Burney Kieke ◽

...

Keyword(s):

Influenza Vaccine ◽

Bayesian Methods ◽

Respiratory Illness ◽

The United States ◽

Vaccine Effectiveness ◽

Bayesian Estimates ◽

Live Attenuated Influenza Vaccine ◽

Percentage Points ◽

Routine Surveillance ◽

Negative Case

Abstract Background Routine influenza vaccine effectiveness (VE) surveillance networks use frequentist methods to estimate VE. With data from more than a decade of VE surveillance from diverse global populations now available, using Bayesian methods to explicitly account for this knowledge may be beneficial. This study explores differences between Bayesian vs. frequentist inference in multiple seasons with varying VE. Methods We used data from the United States Influenza Vaccine Effectiveness (US Flu VE) Network. Ambulatory care patients with acute respiratory illness were enrolled during seasons of varying observed VE based on traditional frequentist methods. We estimated VE against A(H1N1)pdm in 2015/16, dominated by A(H1N1)pdm; against A(H3N2) in 2017/18, dominated by A(H3N2); and compared VE for live attenuated influenza vaccine (LAIV) vs. inactivated influenza vaccine (IIV) among children aged 2–17 years in 2013/14, also dominated by A(H1N1)pdm. VE was estimated using both frequentist and Bayesian methods using the test-negative design. For the Bayesian estimates, prior VE distributions were based on data from all published test-negative studies of the same influenza type/subtype available prior to the season of interest. Results Across the three seasons, 16,342 subjects were included in the analyses. For 2015/16, frequentist and Bayesian VE estimates were essentially identical (41% each). For 2017/18, frequentist and Bayesian estimates of VE against A(H3N2) viruses were also nearly identical (26% vs. 23%, respectively), even though the presence of apparent antigenic match could potentially have pulled Bayesian estimates upward. Precision of estimates was similar between methods in both seasons. Frequentist and Bayesian estimates diverged for children in 2013/14. Under the frequentist approach, LAIV effectiveness was 62 percentage points lower than IIV, while LAIV was only 27 percentage points lower than IIV under the Bayesian approach. Conclusion Bayesian estimates of influenza VE can differ from frequentist estimates to a clinically meaningful degree when VE diverges substantially from previous seasons.

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