People who become infected with SARS-CoV-2 after being vaccinated against it are likely to have milder and shorter illnesses, according to data from 2 ongoing studies funded by the Centers for Disease Control and Prevention.
Researchers analyzed breakthrough infections among almost 4000 US health care personnel, first responders, and other essential and frontline workers in the Arizona Healthcare, Emergency Response, and Other Essential Workers Surveillance Study (AZ HEROES) and the Research on the Epidemiology of SARS-CoV-2 in Essential Response Personnel (RECOVER) study. Data from the HEROES-RECOVER network previously showed that the Pfizer-BioNTech and Moderna mRNA vaccines reduce the risk of SARS-CoV-2 infection by 90% in real-world settings.
In the new analysis, published in the New England Journal of Medicine, 204 SARS-CoV-2 infections occurred. The majority of cases were among unvaccinated workers—only 5 fully vaccinated and 11 partially vaccinated participants tested positive for the virus between December 14, 2020, and April 10, 2021. The partially or fully vaccinated workers had a 40% lower viral load on average, a 66% lower risk of viral RNA detection for more than 1 week, and a 58% lower risk of fever symptoms than unvaccinated participants who became infected. Their COVID-19 symptoms also subsided about 6 days earlier and they spent 2.3 fewer days sick in bed.
Vaccination likely creates immunological memory responses that reduce viral replication and speed up the elimination of infected cells during breakthrough infections, the study’s authors noted. However, because so few of these infections occurred, the researchers could not differentiate the attenuating benefits of partial vs full vaccination.
“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,” Sarang Yoon, DO, RECOVER’s principal investigator, said in a statement. “Those who unfortunately got COVID-19 despite being vaccinated were still better off than those who didn’t.”