Real-world study by CDC finds Pfizer, Moderna vaccines reduce risk of infection by 90%

Virus Outbreak Vaccine
Posted at 11:40 AM, Mar 29, 2021

WASHINGTON, D.C. — A new study from the Centers for Disease Control and Prevention (CDC) found that mRNA COVID-19 vaccines are nearly as effective in the real world as they were in controlled studies.

The study published Monday looked at the effectiveness of the Pfizer-BioNTech and Moderna vaccines among health care personnel, first responders and other essential workers in six states over a 13-week period from December 14 to March 13.

The study showed the risk of infection was reduced by 90% two or more weeks after receiving the second dose of the vaccines. When the vaccines were originally studied, they were shown to be about 95% effective after the second dose.

Following a single dose of either vaccine, the participants’ risk of infection with the coronavirus was reduced by 80% two or more weeks after vaccination. Though, two doses are still recommended.

The CDC says these findings are consistent with those from Phase 3 clinical trials conducted with the vaccines before they received emergency use authorizations from the Food and Drug Administration (FDA).

Those clinical trials evaluated vaccine efficacy against COVID-19 disease, while this study evaluated vaccine effectiveness against infection, including infections that did not result in symptoms.

This study is the U.S. government’s first assessment of how the vaccines have been working beyond the initial experiments conducted by drugmakers. Officials say study results can sometimes change when vaccines are used in larger and more diverse populations outside of controlled groups.

“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 CDC says the study also demonstrated that the two mRNA vaccines can reduce the risk of all SARS-CoV-2 infections, not just symptomatic infections.

“This is important because preventing both asymptomatic and pre-symptomatic infections among health care workers and other essential workers through vaccination can help prevent the spread of SARS-CoV-2 to those they care for or serve,” wrote the CDC.

The CDC says this study is the first of many planned COVID-19 vaccine effectiveness studies the agency is conducting to evaluate the benefits of vaccines in various populations and across different outcomes, such as preventing infections, doctor’s visits, hospitalizations, or deaths.