Brian Hagberg
A study conducted by the Centers for Disease Control and Prevention suggests the two-dose COVID-19 vaccines made by Moderna and Pfizer-BioNTech are 90 percent effective in preventing infection in a real-world setting.
The study looked at the effectiveness of Pfizer-BioNTech and Moderna mRNA vaccines in preventing SARS-CoV-2 infections among 3,950 study participants, consisting of health care personnel, first responders and other frontline workers, in six states over a 13-week period from December 14, 2020 to March 13, 2021.
Results 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 infection with SARS-CoV-2 was reduced by 80 percent two or more weeks after vaccination.
“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,” CDC Director Dr. Rochelle P. Walensky said in a news release. “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 CDC released the study Monday in Morbidity and Mortality Weekly Report, an online journal published by the CDC.
The vaccine’s effectiveness following two doses was similar to the 95 percent and 94 percent that the Pfizer and Moderna vaccines showed, respectively, during the clinical trials that supported their emergency authorizations. The CDC’s study was not conducted in a way to differentiate the effectiveness between the two vaccines.
None of the study’s participants had previously been infected with COVID. Nearly two-thirds, 62.8 percent, of the participants received both doses of the vaccine during the study period and 12.1 percent had only one dose.
Among those participants who were fully vaccinated, there were 0.04 infections per 1,000 person-days, meaning that among 1,000 people there would be 0.04 infections in a day. For those participants who received only a single dose of the vaccine, there were 0.19 infections per 1,000 person-days.
There were 1.38 infections per 1,000 person-days among unvaccinated participants.
The CDC said this is the first of many studies that will be conducted to determine vaccine effectiveness.
