COVID-19 vaccines coverage and effectiveness against SARS-CoV-2 infection among residents in the largest Health Authority of Lazio region (Italy): a population-based cohort study.

BACKGROUND: The waning of the protective effect of COVID-19 vaccines and timing of booster doses are debated. METHODS: Population-based cohort study in the largest Health-Authority of Lazio region, Italy, on 946,156 residents aged 12+ (study period: 1 January 2021-10 January 2022). Vaccine effectiveness (VE) against any SARS-CoV-2 infection (symptomatic or asymptomatic) was estimated through multivariable negative-binomial models using unvaccinated person-time as a reference. RESULTS: The primary vaccination cycle was completed by 81% of residents; of these, 45% received a booster dose. Vaccine coverages were lower for foreigners, and people living in deprived areas, families with children aged 0-11, and households size 1 or 6+. Overall, VE waned from 71% (95% Confidence Interval (CI) 70-73%) 1 month after the second dose to 43% (CI 41-45%) after 4 months and 24% (CI 21-27%) after 6 months, especially in the elderly aged 70+. We observed a prompt restore of VE 15-19 days after the booster dose (69%, CI 67-70%). CONCLUSIONS: Our results support the recommendation of a booster dose 4 months after completion of the primary cycle, giving priority to elderly and fragile individuals. The lower vaccine coverage among social disadvantaged subgroups suggests the need of targeted communication and interventions.

Effectiveness of the Comirnaty and the Vaxzevria vaccines in preventing SARS-CoV-2 infection among residents in Lazio region (Italy).

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.