Revista de patología clínica y experimental

Abstracto

The Association of Vaccination and the Incidence of New Cases of COVID-19 among Health Care Workers, December 16, 2020, through May 4, 2021

James Dawahare, Rishi Raj, Gregory Green, Richard Hom, Fadi Al Akhrass, Nina Reynolds, Christina Al Akhrass

Background: Evidence is limited regarding the effectiveness of the two-dose messenger RNA (mRNA) vaccines BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) in preventing symptomatic severe acute respiratory coronavirus 2 (SARS-CoV-2) infection when vaccinated and unvaccinated groups are similar in size.

Aim: New research is needed to demonstrate the Vaccine Effectiveness (VE) in health care settings with relatively low vaccination rates and where the follow-up periods are more extended than prior research. This study uses a "Real-World" cohort of HCWs and provides insight into the effectiveness of the mRNA vaccines against symptomatic SARS-CoV-2 infection.

Methods: This was a single-center retrospective cohort study evaluating association between vaccinations with BNT162b2 and mRNA-1273 vaccines and incidence of new cases of symptomatic SARS-CoV-2 infections among HCWs between December 16, 2020, and May 4, 2021. Daily screening for symptoms was done using electronic “Fast Pass” and nasopharyngeal (NP) Polymerase chain reaction (PCR) confirmed all positive lateral-flow antigen tests. Incidence rate of COVID-19 among vaccinated and unvaccinated HCWs was calculated and VE was defined as 1-Incidence Rate Ratio (IRR). Statistical analysis was done using t-tests for normally distributed continuous variables and χ² tests for categorical variables.

Results: Of the group of HCWs studied, only 52.1% received the mRNA vaccines with 91% of participants receiving the BNT162b2 vaccine. The incidence rate of symptomatic SARS-CoV-2 infection in the fully vaccinated group was 4.14 per 100 000 person-days compared to 95.53 per 100000 person-days in the unvaccinated group (IRR, 0.0433 [95% CI, 0.018-0.1]; VE=95.67%).

Conclusion: Receipt of the authorized mRNA vaccines, essentially BNT16b2, was associated with a significantly lower incidence of symptomatic SARS-CoV-2 infection in the absence of highly vaccination rates and for a median follow-up of 139 days.