Biostatistics doctoral student Nickolas Lewis led the retrospective study of statewide disease-surveillance data on more than 95,000 COVID-19 survivors—including long-term congregate-care (LTCC) residents and workers—in Rhode Island from Mar 1, 2020, to Dec 9, 2021. The survivors were aged 12 and older, and were unvaccinated at the time they tested positive for COVID-19. The main outcome was reinfection at least 90 days after the first positive test.

Researchers found that receipt of two doses of an mRNA COVID-19 vaccine or one dose of a viral-vector vaccine was linked to protection against reinfection of 49% (95% confidence interval [CI], 27% to 65%) among 3,124 LTCC residents, 47% (95% CI, 19% to 65%) among 2,877 LTCC employees, and 62% (95% CI, 56% to 68%) in 94,516 members of the general population during periods dominated by the wild-type, Alpha, and Delta SARS-CoV-2 strains.

The odds of reinfection at 9 months among participants who remained unvaccinated after COVID-19 recovery were 13.0% (95% CI, 12.0% to 14.0%) among LTCC residents, 10.0% (95% CI, 8.8% to 11.5%) among LTCC workers, and 1.9% (95% CI, 1.8% to 2.0%) in the general population, after adjusting for confounding factors and varying infection rates over time.

The study authors said the results can inform COVID-19 vaccination guidelines, especially those relating to LTCC residents and staff. "Individuals who have recovered from COVID-19 and remain unvaccinated should be encouraged to complete vaccinations, as they are eligible, to reduce their risk of reinfection," they wrote.

Joe Hogan, Professor of Biostatistics and co-author of the paper was interviewed by WPRI. Watch the interview below.