Pfizer-BioNTech Coronavirus Disease 2019 Vaccine Effectiveness Against Severe Acute Respiratory Syndrome Coronavirus 2 Infection Among Long-term Care Facility Staff With and Without Prior Infection in New York City, January-June 2021

Abstract

Background: Evidence is accumulating of coronavirus disease 2019 (COVID-19) vaccine effectiveness among persons with prior severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Methods: We evaluated the effect against incident SARS-CoV-2 infection of (1) prior infection without vaccination, (2) vaccination (2 doses of Pfizer-BioNTech COVID-19 vaccine) without prior infection, and (3) vaccination after prior infection, all compared with unvaccinated persons without prior infection. We included long-term care facility staff in New York City aged <65 years with weekly SARS-CoV-2 testing from 21 January to 5 June 2021. Test results were obtained from state-mandated laboratory reporting. Vaccination status was obtained from the Citywide Immunization Registry. Cox proportional hazards models adjusted for confounding with inverse probability of treatment weights.

Results: Compared with unvaccinated persons without prior infection, incident SARS-CoV-2 infection risk was lower in all groups: 54.6% (95% confidence interval, 38.0%-66.8%) lower among unvaccinated, previously infected persons; 80.0% (67.6%-87.7%) lower among fully vaccinated persons without prior infection; and 82.4% (70.8%-89.3%) lower among persons fully vaccinated after prior infection.

Conclusions: Two doses of Pfizer-BioNTech COVID-19 vaccine reduced SARS-CoV-2 infection risk by ≥80% and, for those with prior infection, increased protection from prior infection alone. These findings support recommendations that all eligible persons, regardless of prior infection, be vaccinated against COVID-19.

Keywords: COVID-19 vaccine effectiveness; SARS-CoV-2 reinfection; long-term care facilities.

Figure 1.

CONSORT (Consolidated Standards of Reporting Trials) diagram showing initial eligible population, exclusion criteria, and final analytic samples for primary and secondary analyses. The positivity assumption was violated if there were not exposed and unexposed persons in each confounder stratum. Abbreviations: ECLRS, New York State Electronic Clinical Laboratory Reporting System; NYC, New York City; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 2.

Percentage reduction in risk of severe acute respiratory syndrome coronavirus 2 infection, compared with unvaccinated persons without prior infection, by vaccination and prior infection status. Study population included long-term care facility staff in New York City from December 2020 to June 2021. Percentages were calculated as (1 − hazard ratio) × 100 and are shown on a log scale. Unvaccinated was defined as having received zero doses of any coronavirus disease 2019 (COVID-19) vaccine; single-dose vaccinated, as ≥14 days after receipt of the first dose of Pfizer-BioNTech COVID-19 vaccine until receipt of the second dose; and fully vaccinated, as ≥14 days after receipt of the second dose of Pfizer-BioNTech COVID-19 vaccine. In the primary analysis, person-time for vaccinated persons began ≥14 days after receipt of the second dose, and person-time for unvaccinated persons began on the earliest date when persons could have been fully vaccinated. In the secondary analysis, person-time began for all individuals on the date of the first on-site vaccination clinic held at any of the long-term care facilities where they worked.