BACKGROUND

It is not known if widespread vaccination can prevent the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in subpopulations at high risk, like older adults in nursing homes (NH).

OBJECTIVE

The objective of the study was to know if coronavirus disease 2019 (COVID-19) outbreaks can occur in NH with high vaccination coverage among its residents.

METHODS

We identified, using national professional networks, NH that suffered COVID-19 outbreaks despite having completed a vaccination campaign, and asked them to send data, using predefined collecting forms, on the number of residents exposed, their vaccination status and the number, characteristics, and evolution of patients infected. The main outcome was to identify outbreaks occurring in NH with high vaccine coverage. Secondary outcomes were residents' risk of being infected, developing severe disease, or dying from COVID-19 during the outbreak. SARS-CoV-2 infection was defined by a positive reverse transcriptase-polymerase chain reaction. All residents were serially tested whenever cases appeared in a facility. Unadjusted secondary attack rates, relative risks, and vaccine effectiveness during the outbreak were estimated.

RESULTS

We identified 31 NH suffering an outbreak during March-April 2021, of which 27 sent data, cumulating 1,768 residents (mean age 88.4, 73.4% women, 78.2% fully vaccinated). BNT162b2 was the vaccine employed in all NH. There were 365 cases of SARS-CoV-2 infection. Median secondary attack rates were 20.0% (IQR 4.4%-50.0%) among unvaccinated residents and 16.7% (IQR 9.5%-29.2%) among fully vaccinated ones. Severe cases developed in 42 of 80 (52.5%) unvaccinated patients, compared with 56 of 248 (22.6%) fully vaccinated ones (relative risks [RR] 4.17, 95% CI: 2.43-7.17). Twenty of the unvaccinated patients (25.0%) and 16 of fully vaccinated ones (6.5%) died from COVID-19 (RR 5.11, 95% CI: 2.49-10.5). Estimated vaccine effectiveness during the outbreak was 34.5% (95% CI: 18.5-47.3) for preventing SARS-CoV-2 infection, 71.8% (58.8-80.7) for preventing severe disease, and 83.1% (67.8-91.1) for preventing death.

CONCLUSIONS

Outbreaks of COVID-19, including severe cases and deaths, can still occur in NH despite full vaccination of a majority of residents. Vaccine remains highly effective, however, for preventing severe disease and death. Prevention and control measures for SARS-CoV-2 should be maintained in NH at periods of high incidence in the community.