IntroductionThe I-MOVE-COVID-19 and VEBIS hospital networks have been measuring COVID-19
vaccine effectiveness (VE) in participating European countries since early 2021.AimWe
aimed to measure VE against PCR-confirmed SARS-CoV-2 in patients ≥ 20 years hospitalised
with severe acute respiratory infection (SARI) from December 2021 to July 2022 (Omicron-dominant
period).MethodsIn both networks, 46 hospitals (13 countries) follow a similar test-negative
case-control protocol. We defined complete primary series vaccination (PSV) and first
booster dose vaccination as last dose of either vaccine received ≥ 14 days before
symptom onset (stratifying first booster into received < 150 and ≥ 150 days after
last PSV dose). We measured VE overall, by vaccine category/product, age group and
time since first mRNA booster dose, adjusting by site as a fixed effect, and by swab
date, age, sex, and presence/absence of at least one commonly collected chronic condition.ResultsWe
included 2,779 cases and 2,362 controls. The VE of all vaccine products combined against
hospitalisation for laboratory-confirmed SARS-CoV-2 was 43% (95% CI: 29-54) for complete
PSV (with last dose received ≥ 150 days before onset), while it was 59% (95% CI: 51-66)
after addition of one booster dose. The VE was 85% (95% CI: 78-89), 70% (95% CI: 61-77)
and 36% (95% CI: 17-51) for those with onset 14-59 days, 60-119 days and 120-179 days
after booster vaccination, respectively.ConclusionsOur results suggest that, during
the Omicron period, observed VE against SARI hospitalisation improved with first mRNA
booster dose, particularly for those having symptom onset < 120 days after first booster
dose.
