COVID-19 vaccination reduces asymptomatic infection risk


Receiving a COVID-19 vaccination dramatically reduces the chances of contracting the virus, either in symptomatic or asymptomatic form.
That’s according to new research from St. Jude Children’s Research Hospital published in JAMA on Thursday. Almost 8,000 hospital workers—both vaccinated and unvaccinated—were regularly tested between Dec. 2019 to March 2020.

The results come as demand for the vaccine slows in part due to hesitency, and a recent White House push to get at least 70% of U.S. adults one dose by July 4th.
Overall, vaccination reduced the risk of asymptomatic and symptomatic COVID-19 infection by 79% in vaccinated employees compared with their unvaccinated colleagues. An analysis of asymptomatic infections alone found vaccination reduced the risk by 72%.

Protection was even greater for employees who completed two doses. A week or more after receiving the second dose, vaccinated employees were 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%.

“There is still is a knowledge gap about whether this vaccine is effective in in protecting people from getting any infection, including asymptomatic infections,” said Li Tang, a biostatistics researcher at St. Jude Children’s Research Hospital. “We know very little about those secret carriers with asymptomatic infections, but they may play a critical role in the transmission and in making this pandemic so severe.”

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 upon testing. The asymptomatic cases included 20 employees who had received one vaccine dose and three who tested positive within seven days of the second dose.

Meanwhile, this week HHS said there’s almost $1 billion available to go to rural health providers to not only vaccinate and test residents, but to combat vaccine hesitancy through campaigns and hiring outreach workers. President Joe Biden also set a goal to vaccinate 70% of U.S. adults with at least one dose before July 4th. And earlier in April a coalition of 60 hospitals and other healthcare systems, including the Cleveland Clinic and Mayo Clinic, launched a campaign to increase the number of people vaccinated.
The study is among the first to show an association between COVID-19 vaccination and fewer asymptomatic infections, and could be instrumental in building confidence around vaccines. And while the reduction in contraction of the virus post vaccination is good news, the St. Jude researchers say it’s still an unknown if asymptomatic carriers can transmit the virus, which is an important point for employers to keep in mind as workers are allowed to come back to work in person.

“And that’s why we keep saying that the use of masks, some physical distance and washing your hands is important,” said Dr. Diego Hijano in St. Jude’s department of infectious diseases. “You’re going to return to a place where some people are not going to be vaccinated – either because they have a contraindication, or they have chosen not to receive the vaccine – and you need to protect those individuals.”



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Marie Maynes
Marie Maynes is a Sports enthusiast and writes for the Sports section of ANH.