A new Centers for Disease Control and Prevention (CDC) study provides strong evidence that mRNA COVID-19 vaccines are highly effective in preventing SARS-CoV-2 infections, according to the health agency.
The study examined the effectiveness of Pfizer-BioNTech and Moderna mRNA vaccines in preventing COVID-19 infections among 3,950 study participants in six states over a 13-week period from Dec. 14, 2020 to March 13.
The analysis took place in real-world conditions covering health care personnel, first responders and other essential workers– groups that are more likely than the general population to be exposed to the virus because of their occupations.
The findings showed that following the second dose of vaccine — the recommended number of doses — risk of infection was reduced by 90 percent two or more weeks after vaccination.
Following a single dose of either vaccine, the participants’ risk of COVID-19 infection was reduced by 80 percent two or more weeks after vaccination.
The CDC says it takes about two weeks following each dose of vaccine for the body to produce antibodies that protect against infection. As a result, people are considered “partially vaccinated” two weeks after their first dose of mRNA vaccine and “fully vaccinated” two weeks after their second dose.
“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 P. Walensky, MD, MPH.
“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.”
The study also provided positive news about partial, one-dose vaccination. The CDC says the one-dose estimate of this study is consistent with other recent studies following the first dose of Pfizer-BioNTech vaccine among health care providers.
Studies conducted in the United Kingdom and Israel showed that one dose was about 70 percent and 60 percent effective, respectively, against COVID-19.
The current results provide reassurance that people start to develop protections due to the vaccine two weeks after their first dose, says the health agency. The greatest protection was seen among those who had received both recommended doses of the vaccine.
“This study is the first of many planned COVID-19 vaccine effectiveness studies CDC is conducting to evaluate the benefits of COVID-19 vaccines in various populations and across different outcomes, such as preventing infections, doctor’s visits, hospitalizations or deaths,” according to the health agency.
“Results from these studies assist the medical and public health experts on the Advisory Committee on Immunization Practices and CDC to make important vaccine policy decisions aimed at saving lives.”