COVID-19 Vaccine Associated With Fewer Asymptomatic SARS-CoV-2 Infections


The study is one of the first to show an association between COVID-19 vaccination and fewer asymptomatic infections, according to the authors.

A research letter from St. Jude’s Children’s Research Hospital found that vaccination dramatically reduced COVID-19 symptomatic and asymptomatic infections in employees compared with their unvaccinated peers.

The study is one of the first to show an association between COVID-19 vaccination and fewer asymptomatic infections, according to the authors. Clinical trial data suggested that the 2-dose vaccine regimen reduced symptomatic disease, including hospitalization and death, but an association with reduced asymptomatic infection was unclear.

“While further research is needed, by preventing infections, including in people who have no symptoms, there is a high possibility that vaccination will decrease transmission of SARS-CoV-2,” said Diego Hijano, MD, of the St. Jude Department of Infectious Diseases, in a press release.

The study involved 5217 St. Jude employees who were eligible under Tennessee state guidelines for vaccination between December 17, 2020, and March 20, 2021. More than 58% of employees were vaccinated during that period, and most workers received both doses, according to the press release.

Overall, vaccination reduced the risk of asymptomatic and symptomatic SARS-CoV-2 infection by 79% in vaccinated employees compared with their unvaccinated colleagues. Further, an analysis of asymptomatic infections alone found vaccination reduced the risk by 72%.

Protection was greater for employees who completed 2 doses, according to the study. A week or more after receiving the second dose, vaccinated employees were found to be 96% less likely than unvaccinated workers to become infected with SARS-CoV-2. When researchers looked just at asymptomatic infections, vaccination reduced the risk by 90%, according to the study.

During the study, 236 of the 5217 employees included in the analysis tested positive for SARS-CoV-2. Additionally, they included 185 unvaccinated employees and 51 of the 3052 workers who had received at least 1 dose of the vaccine.

Almost half of the positive cases (108) reported no symptoms upon testing. The asymptomatic cases included 20 employees who had received 1 vaccine dose and 3 who tested positive within 7 days of the second dose.

“The results are a reminder of the many hidden cases in the population, which makes containing the virus a big challenge,” said corresponding author Li Tang, PhD, in the press release.

The study group included a cross-section of employees in regard to race and gender, with more than 80% of employees younger than 65 years of age. The vaccinated group included a higher percentage of health care staff (47%) than the unvaccinated employees (25.7%).


COVID-19 vaccine is associated with fewer asymptomatic SARS-CoV-2 infections. St. Jude Children’s Research Hospital. Published May 6, 2021. Accessed May 10, 2021.

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