Interim analysis of COVID-19 vaccine effectiveness against … – European Union

A retrospective cohort was constructed from linked electronic health records (EHR) in each country. Country- specific (level) relative VE (rVE) was estimated on a monthly basis, using a study period covering an eight-week follow-upperiod.Eachmonththestudyperiodwasshiftedforwardtothe followingmonth.Countryestimateswere then pooledtogether. The study period coveredin this report is April 2022 to March 2023. The rVE of first, second and third booster doses was estimated and compared to the VE of complete primary vaccination received at least 24 weeks ago (24 weeks).

BetweenApril2022andMarch2023,thenumberofindividualsincludedintheanalysisineachstudyperiodvaried between 0.5 million and 1.3 million individuals with complete primary vaccination series 24 weeks ago but without a booster, between 3.1 million and 13.2 million individuals completely vaccinated with a first booster, between no individuals and 6.8 million individuals completely vaccinated with a second booster and between no individualsand0.7millioncompletelyvaccinatedwithathirdbooster.About31 900hospitalisationsduetoCOVID- 19 and 13 100 COVID-19-related deaths were recorded across the different sites throughout the study period.

The highest number of person-months contributing to the analysis was observed for Belgium and Portugal, followed by Norway, Denmark, Navarre (Spain), and Luxembourg. In persons aged80 years, Belgium and Portugalrolledoutthesecondboosterdoseoverspring2022andthethirdbooster doseinautumn2022,whilethe administration of a second booster began in autumn 2022 in the remaining participating countries.

At the beginning of the study period, most of the study population had received a first booster dose, while the proportionofindividualscompletelyvaccinatedwithprimarydoseswithoutaboosterwasverylow,especiallyin

65years(Figure2).Asecondboosterdosewasadministratedinitiallyinpersonsaged80yearsfromJuly2022 onwardsinmostparticipatingcountries exceptforBelgiumandPortugal,whereitstartedearlierinspring2022in those aged80 followed by 5079year olds in autumn 2022. In these two countries, the third booster dose was then deployed in80-year-olds in OctoberNovember 2022.

Compared to complete primary vaccination, the first boosterdose rVE against hospitalisation due to COVID-19 was mostly 50% between April 2022 and March 2023 in all age groups (with a few point estimates >50%). It waned 12 weeks after administration and dropped even lower after 24 weeks. In the most recent estimate, between February and March 2023, the first booster (mostly administered >24 weeks) showed little to no added protection:rVEestimatesrangedbetween-1317%,amongthedifferentagegroups.VEestimatesagainstCOVID- 19-related mortality were similar, although estimates had high uncertainty due to a low number of events, particularly in the groups <65 years.

Compared to complete primary vaccination, rVE of a second boosterrestored protection shortly after administration in the autumn of 2022 in65-year-olds, to 7679% against hospitalisation due to COVID-19 and to 7685% against COVID-19 related death. Relative vaccine effectiveness also waned with time, falling to 50% after24weeks.Inthemostrecentestimate,between FebruaryandMarch2023,rVEofthesecondboosterranged between 3349% against hospitalisation and 5063% against mortality 1224 weeks after administration and between3.543%againsthospitalisationand50%againstmortality(estimatedonlyin80yearolds)after24weeks.

Comparedtocompleteprimaryvaccination,rVEofthethirdboostercouldonlybeestimatedinindividualsaged

80 years in Portugal and Belgium. Relative vaccine effectiveness against hospitalisation due to COVID-19 was 72%shortlyafteradministration but wanedrapidly, being zero beyond12 weeks of administration. The lowerrVE could possibly be related to the higher proportion of individuals with comorbidities among those with a third booster(beingapopulationthathadpreviouslyacceptedasecondboosterinthespringof2022). Relativevaccine effectiveness against mortality was 64% initially (<12 weeks after administration) and waned rapidly thereafter (<50% 1224 weeks after administration with large confidence intervals). In FebruaryMarch 2023, the rVE of a third booster 1224 weeks after administration was 3% (95% CI: -26 709; 100).

Overall,resultsindicatedthat boosterdosesrestoredprotectionshortlyafteradministration,butitwanedinthe period up to 24 weeks after administration.

During the autumn of 2022, the effectiveness of third booster doses (in Portugal and Belgium where second boosters had been administered over spring 2022) and second booster doses (in those remaining participating countries)weresimilar.Thisresultsuggeststhatthetimesincethelastdosewasmoreimportantthanthetotal number of doses administered in the level of protection against both COVID-19 hospitalisation and death.

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Interim analysis of COVID-19 vaccine effectiveness against ... - European Union