A CDC study examining the effectiveness of the Pfizer and Moderna COVID-19 vaccines found “strong evidence” that the vaccines are “highly effective” in preventing infections in real-world conditions among health care personnel, first responders and other essential workers that are more likely than the general population to be exposed to the virus.
The Centers for Disease Control announced its study findings on Monday, and the results also indicate a high degree of protection associated with a single dose of the two-dose vaccine.
The study involved 3,950 participants in six states over a 13-week period from Dec. 14, 2020 to March 13, 2021.
The results, according to the CDC, showed that following the second dose the risk of infection was reduced by 90 percent two or more weeks after vaccination., and following a single dose of either vaccine the risk of infection was reduced by 80 percent two or more weeks after vaccination.
The CDC said the findings are consistent with those from Phase 3 clinical trials conducted with the vaccines before they received emergency use authorization from the FDA.
The clinical trials evaluated vaccine efficacy against COVID-19 disease, while the CDC study evaluated effectiveness against infection, including infections that did not result in symptoms.
The study participants self-collected nasal swabs each week for testing, regardless of whether they had developed symptoms of illness. The majority of infections (58 percent) detected in the study occurred among people whose infections were identified by testing before they developed symptoms or knew they were infected.
“This study shows that our national vaccination efforts are working. The authorized mRNA COVID-19 vaccines provided early, substantial real-world protection against infection for our nation’s health care personnel, first responders, and other frontline essential workers,” said CDC Director Rochelle Walensky. “These findings should offer hope to the millions of Americans receiving COVID-19 vaccines each day and to those who will have the opportunity to roll up their sleeves and get vaccinated in the weeks ahead. The authorized vaccines are the key tool that will help bring an end to this devastating pandemic.”