Messenger RNA vaccines lower risk for asymptomatic infection, study finds


Participants who received two doses of a messenger RNA COVID-19 vaccine were 80% less likely to test positive for asymptomatic SARS-CoV-2, according to real-world study results published in Clinical Infectious Diseases.

Even after one dose, the risk for asymptomatic infection was reduced by 79%, researchers reported. The two messenger RNA vaccines authorized for use in the United States are made by Pfizer-BioNTech and Moderna.

Messenger RNA vaccines lower risk for asymptomatic infection, study finds

“As people are undergoing their routine care and they're caring for patients, if they have a preprocedure testing protocol like we do, they can take some comfort in that these vaccines will decrease the likelihood of infection for those patients,” Aaron J. Tande, MD, consultant in the division of infectious diseases and associate professor of medicine at the Mayo Clinic College of Medicine, told Healio.

“For the broader COVID-19 landscape, we think that a good proportion — some studies have estimated 50% of infections — arise from people who are asymptomatic or presymptomatic. This suggests that the vaccines not only prevent severe disease but can also prevent subsequent transmissions from people [who] are asymptomatic because they are simply less likely to become infected,” Tande said.

Tande and colleagues performed a retrospective cohort study of asymptomatic adult patients who underwent a total of 48,333 preprocedural SARS-CoV-2 screening tests from Dec. 17, 2020, to Feb. 8, 2021. They analyzed the RR of a positive SARS-CoV-2 test among asymptomatic people who had received a vaccine dose compared with those who had not yet been vaccinated.

A positive SARS-CoV-2 test result was identified in 42 (1.4%) of the 3,006 tests given to vaccinated patients and 1,436 (3.2%) of the 45,327 tests given to unvaccinated patients (RR = 0.44; 95% CI, 0.33-0.6). The risk for asymptomatic SARS-CoV-2 infection was lower among individuals more than 10 days after their first dose (RR = 0.21; 95% CI, 0.12-0.37) and more than 0 days after their second dose (RR = 0.2; 95% CI, 0.09-0.44) compared with unvaccinated individuals.

Tande said further studies are needed to address the reduction in COVID-19 spread following vaccination over larger time periods.

“We need to get larger studies to confirm this and look at specific subgroups of patients. Do people who are immunocompromised have the same results?” Tande said.