The investigators also found that the risk of spreading disease may be lower amongst those with breakthrough infections.
A nationwide study published in the New England Journal of Medicine found that patients who had received mRNA COVID-19 vaccines had up to 91% lower likelihood of developing the disease compared to individuals who are unvaccinated. Further, in the remaining vaccinated patients that did develop an infection, known as breakthrough cases, the study results suggest the duration of infection and the severity of symptoms are both reduced.
The study, which builds off of preliminary data released in March by the CDC, was designed to measure infection rates and risks associated with vaccinated individuals on the front lines of the pandemic. The investigators recruited 3975 participants at 8 sites, all of whom submitted samples weekly for COVID-19 testing between December 13, 2020 and April 10, 2021.
According to the results, patients that were fully vaccinated, defined as those who had received their second dose at least 2 weeks earlier, had a 91% lower risk of infection. Those that were partially vaccinated—having received the first dose at least 2 weeks earlier but not the second—had their risk decreased by 81%.
“We gave these vaccines to some of the highest risk groups in this country—doctors, nurses, and first responders,” said Sarang Yoon, DO, assistant professor at the University of Utah Rocky Mountain Center for Occupational and Environmental Health, in a press release. “These are the people who are getting exposure to the virus day in and day out, and the vaccine protected them against getting the disease. Those who unfortunately got COVID-19 despite being vaccinated were still better off than those who didn't [receive a vaccine].”
Only 16 of the participants who were fully or partially vaccinated eventually tested positive for SARS-CoV-2. Patients with breakthrough infections had significantly reduced symptoms, including a 58% reduction in the presence of fever, a 60% decrease in days spent sick in bed, a reduction of virus detection from 8.9 days to 2.7 days, and no chance of hospitalization.
The investigators also found that the risk of spreading disease may be lower amongst those with breakthrough infections. Infected study participants that had been either fully or partially vaccinated had 40% less detectable virus in the nose and spent 6 fewer days with any amount of detectable virus in the nose compared to unvaccinated individuals.
“I hope these findings reassure the public that mRNA COVID-19 vaccines are safe and protect us from this severe disease,” Yoon said in the release.
mRNA vaccines slash risk of COVID-19 infection by 91% in fully vaccinated people [news release]. EurekAlert; July 6, 2021. Accessed July 8, 2021. https://www.eurekalert.org/pub_releases/2021-07/uouh-mvs070621.php