Vaccination significantly reduced symptomatic and asymptomatic COVID-19 infections among employees at St. Jude Children’s Research Hospital compared to their unvaccinated peers, according to a research letter published today in the Journal of the American Medical Association.
The study is among the first to show an association between COVID-19 vaccination and fewer asymptomatic infections. When the Pfizer-BioNTech BNT162b2 vaccine was approved for use in the United States, the vaccine was reported to be highly effective in preventing lab-confirmed COVID-19. Data from clinical trials suggest that the two-dose regimen reduces symptomatic illness, including hospitalization and death. But an association with reduced asymptomatic infection was unclear.
“Although more research is needed, by preventing infections, including in people who have no symptoms, there is a strong possibility that vaccination will decrease the transmission of SARS-CoV-2,” said Diego Hijano, MD, of the Department of St. Jude. Infectious diseases. He and Li Tang, Ph.D., of St. Jude Biostatistics, are the original authors of the report. Tang is also the corresponding author.
The study involved 5,217 St. Jude employees who were eligible under the state of Tennessee guidelines for immunization between December 17, 2020 and March 20, 2021. More than 58% of employees were vaccinated during that time. period. Most workers received both doses.
Overall, vaccination reduced the risk of asymptomatic and symptomatic SARS-CoV-2 infection by 79% in vaccinated workers compared to their unvaccinated colleagues. An analysis of asymptomatic infections alone revealed that vaccination reduced the risk by 72%.
The protection was even greater for employees who completed two doses. A week or more after receiving the second dose, vaccinated workers were 96% less likely than unvaccinated workers to be infected with SARS-CoV-2. When researchers looked only at asymptomatic infections, vaccination reduced the risk by 90%.
Testing for SARS-CoV-2 infections
The research stems from a program that executives in St. Jude launched in March 2020 to protect patients and employees from the pandemic virus.
The effort included targeted testing for employees with symptoms of COVID-19 or known exposure to the pandemic virus. The plan also called for routine laboratory testing of asymptomatic employees. Nasal swabs were taken at least once a week from self-reported asymptomatic workers on campus to perform a polymerase chain reaction to detect asymptomatic SARS-CoV-2 infection.
“This study was made possible because St. Jude invested in resources to determine how best to control the disease and protect our patients and employees,” Tang said. “Few places then or now offer asymptomatic tests this broad.”
Hijano said, “The testing has been invaluable to the institutional COVID-19 mitigation plan. Ultimately, the testing also serves as a unique tool that helps fill critical knowledge gaps.”
Results in figures
During the study, 236 of the 5,217 employees included in the analysis tested positive for SARS-CoV-2. They included 185 unvaccinated employees and 51 of the 3,052 workers who had received at least one dose of the vaccine.
Almost half of the positive cases, 108, reported no symptoms during testing. Asymptomatic cases included 20 employees who had received one dose of vaccine and three who had tested positive within seven days of the second dose. “The results are reminiscent of the many cases hidden in the population, which makes controlling the virus a major challenge,” Tang said.
The study group included a representative sample of employees with respect to race and gender. Over 80% of employees were under 65. The vaccinated group included a higher percentage of health workers, 47%, than unvaccinated workers, 25.7%.
Authors and funding
The principal authors are James Hoffman, Pharm.D., And Randall Hayden, MD, of St. Jude. The other authors are Aditya Gaur, Terrence Geiger and Ellis Neufeld, all of St. Jude.
The research was funded in part by ALSAC, the St. Jude fundraising and awareness organization.