CDC: mRNA vaccines reduce risk of infection by 91% for fully vaccinated

For fully vaccinated individuals, the Pfizer and Moderna mRNA COVID-19 vaccines authorized by FDA lower the risk of infection by 91%, CDC reported this week.  

“Findings from the extended timeframe of this study add to accumulating evidence that mRNA COVID-19 vaccines are effective and should prevent most infection—but that fully vaccinated people who still get COVID-19 are likely to have milder, shorter illness and appear to be less likely to spread the virus to others,” said CDC Director Rochelle Walensky, MD, MPH, in a news release. “These benefits are another important reason to get vaccinated.” 

The report is based on 4 weeks of additional data from CDC’s HEROES-RECOVER study of health care workers, first responders, frontline workers, and other essential workers. Preliminary results from the study were first announced in March 2021. In the new findings, nearly 4,000 participants completed weekly SARS-CoV-2 testing, from December 13, 2020, to April 10, 2021, in eight U.S. locations. If the tests came back positive, the specimens were further tested to determine the amount of detectable virus in the nose and the number of days that participants tested positive. Participants were followed over time, and the data were analyzed according to vaccination status.  

To evaluate vaccine benefits, the study investigators accounted for the circulation of SARS-CoV-2 viruses in the area and how consistently participants used personal protective equipment at work and in the community.  

Once fully vaccinated, participants’ risk of infection was reduced by 91%. After partial vaccination, participants’ risk of infection was reduced by 81%. The study findings support CDC’s recommendation to get fully vaccinated against COVID-19 as soon as possible.