Impact of the Coronavirus Disease 2019 (COVID-19) Vaccine on Asymptomatic Infection Among Patients Undergoing Preprocedural COVID-19 Molecular Screening

Abstract

Background: Several vaccines are now available under emergency use authorization in the United States and have demonstrated efficacy against symptomatic COVID-19. Vaccine impact on asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is largely unknown.

Methods: We conducted a retrospective cohort study of consecutive, asymptomatic adult patients (n = 39 156) within a large US healthcare system who underwent 48 333 preprocedural SARS-CoV-2 molecular screening tests between 17 December 2020 and 8 February 2021. The primary exposure of interest was vaccination with ≥1 dose of an mRNA COVID-19 vaccine. The primary outcome was relative risk (RR) of a positive SARS-CoV-2 molecular test among those asymptomatic persons who had received ≥1 dose of vaccine compared with persons who had not received vaccine during the same time period. RR was adjusted for age, sex, race/ethnicity, patient residence relative to the hospital (local vs nonlocal), healthcare system regions, and repeated screenings among patients using mixed-effects log-binomial regression.

Results: Positive molecular tests in asymptomatic individuals were reported in 42 (1.4%) of 3006 tests and 1436 (3.2%) of 45 327 tests performed on vaccinated and unvaccinated patients, respectively (RR, .44; 95% CI, .33-.60; P < .0001). Compared with unvaccinated patients, risk of asymptomatic SARS-CoV-2 infection was lower among those >10 days after the first dose (RR, .21; 95% CI, .12-.37; P < .0001) and >0 days after the second dose (RR, .20; 95% CI, .09-.44; P < .0001) in the adjusted analysis.

Conclusions: COVID-19 vaccination with an mRNA-based vaccine showed a significant association with reduced risk of asymptomatic SARS-CoV-2 infection as measured during preprocedural molecular screening. Results of this study demonstrate the impact of the vaccines on reduction in asymptomatic infections supplementing the randomized trial results on symptomatic patients.

Keywords: COVID-19; SARS-CoV-2; asymptomatic; vaccination.

Figure 1.

Survival analysis by time-to-preprocedural positive COVID-19 test after receiving first dose of vaccination, by total doses received. A person who received their first dose of vaccine on 1 January 2021, their second dose on 24 January 2021, and then had a positive molecular COVID-19 test on 26 January 2021 would appear on both the red (1-dose) and blue (2-dose) lines with the event on day 25 on the x-axis (event occurred 25 days after first dose). Abbreviation: COVID-19, coronavirus disease 2019.

Figure 2.

Adjusted RR (with 95% CIs) comparing preprocedural COVID-19 molecular screening percent positive by vaccination status and timing. *Significant at P < .001. RR adjusted for age, sex, race/ethnicity, and patient residence in the hospital Health Referral Region (local vs nonlocal). Abbreviations: CI, confidence interval; COVID-19, coronavirus disease 2019; RR, relative risk.