mRNA COVID vaccination tied to 80% lower risk of asymptomatic infection
A real-world Mayo Clinic study shows a link between vaccination with two doses of an mRNA-based COVID-19 vaccine—either Pfizer/BioNTech or Moderna—and an 80% lower risk of asymptomatic infection.
The retrospective cohort study, published yesterday in Clinical Infectious Diseases, involved 39,156 asymptomatic adult COVID-19 patients screened for SARS-CoV-2 infection using 48,333 preprocedural tests from Dec 17, 2020, to Feb 8, 2021.
Forty-two (1.4%) of 3,006 tests of patients who had received at least one dose of vaccine were positive for COVID-19, compared with 1,463 (3.2%) of 45,327 tests of unvaccinated patients (relative risk [RR], 0.44).
Compared with unvaccinated patients, the risk of asymptomatic COVID-19 was lower among those who had received one dose of vaccine at least 10 days before testing (72% reduction; RR, 0.21) and those who received a second dose (73%; RR, 0.20). But after adjustment for confounding factors, the risk of infection was 80% lower in those who received two doses.
"The results of this study demonstrate the impact of the vaccines on reduction in asymptomatic infections supplementing the randomized trial results on symptomatic patients," the researchers wrote. "From a public health perspective, it will be important to determine if the current recommendations to maintain pre-vaccination behaviors for masking and social distancing will impact vaccine hesitancy."
Mar 10 Clin Infect Dis study