The messenger RNA vaccines from Pfizer-BioNTech and Moderna were 90 percent effective at preventing COVID-19 infections in real-world settings, according to the CDC's Morbidity and Mortality Weekly Report published March 29.
Researchers evaluated the efficacy of the vaccines among 3,950 healthcare personnel, first responders and other essential workers who did not have a previous confirmed COVID-19 case. The majority of participants in the study were fully vaccinated, or received both vaccine doses, and 477 received a single dose.
Between Dec. 14, 2020, and March 12, 2021, participants self-collected nasal swabs and were tested weekly for COVID-19, regardless of whether they were experiencing symptoms.
Findings showed the risk of infection was cut by 90 percent two or more weeks after receiving the second shot. A single dose was linked to an 80 percent reduced risk of infection at least two weeks after it was administered.
A total of 205 people, or 5.2 percent, tested positive during the study period. Of those infections, 58 percent were identified through testing before the person knew they were infected or experienced symptoms — an indicator that the vaccines are effective at reducing the risk of asymptomatic infection, the CDC said.
"These findings indicate that authorized mRNA COVID-19 vaccines are effective for preventing SARS-CoV-2 infection, regardless of symptom status, among working-age adults in real-world conditions," the report said.
To view the full report, click here.