We estimated the effectiveness of Comirnaty and Vaxzevria vaccines among 371,423 residents in Lazio Region (Italy) vaccinated since 27/12/2020, and followed until diagnosis of SARS-CoV-2 infection or 25/4/2021, whichever came first. By the end of follow-up most of the Comirnaty-cohort (60%) had received the second dose at recommended time of 21 days (98%), while the Vaxzevria-cohort had received only one dose. Adjusted hazard ratios of SARS-CoV-2 infection at weekly intervals since the first dose were estimated through a Cox regression model using 0-13 days as reference time-interval. An increase in effectiveness with increasing time since administration was observed for Comirnaty (five-weeks = 81%, 95 %CI 71-88%; three-months = 94%, 95 %CI 84-98%). One dose of Vaxzevria showed an effectiveness of 63% (95 %CI 25-82%) after 7 weeks, although further analyses are needed after complete vaccination with two doses. These results could support the ongoing vaccination campaign by reinforcing evidence-based communication aimed at reducing vaccine hesitancy.
Keywords: Cohort study; Comirnaty; Covid-19; SARS-CoV-2 infection; Vaccine effectiveness; Vaxzevria.
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