A CDC study of 1,843 healthcare workers found that COVID-19 mRNA vaccines from Pfizer-BioNTech and Moderna reduced the risk of infection by 94% among HCWs who were fully vaccinated, according to theThis assessment, conducted in a different study network with a larger sample size from across a broader geographic area than in the clinical trials, independently confirms US vaccine effectiveness findings among healthcare workers that were first reported March 29.
“This report provided the most compelling information to date that COVID-19 vaccines were performing as expected in the real world,” said CDC Director Rochelle P. Walensky, MD, MPH. “This study, added to the many studies that preceded it, was pivotal to CDC changing its recommendations for those who are fully vaccinated against COVID-19.”
Data for this assessment come from a network covering 500,000 HCP across 33 sites in 25 U.S. states, providing additional robust evidence that mRNA vaccines are effective against symptomatic illness in real-world conditions.
The assessment compared vaccination status of participants who tested positive for SARS-CoV-2, the virus that causes COVID-19 (cases) with vaccination status of those who tested negative (controls). Among the 1,843 participants, there were 623 cases and 1,220 controls. Vaccine effectiveness estimates were calculated by comparing the odds of COVID-19 vaccination in cases and controls. The large sample size in this study allowed for a precise vaccine effectiveness estimate with narrower confidence intervals than earlier CDC findings published March 29.
Understanding vaccine effectiveness among HCP is important because they are at higher risk for exposure to SARS-CoV-2 through patient interactions. Vaccination of HCP protects them and their patients against COVID-19 and ensures continuation of critical health care services.
The assessment found that COVID-19 symptomatic illness was reduced by 94% among HCP who were fully vaccinated, defined in this study as seven or more days after receipt of a second vaccine dose, and by 82% among those who were partially vaccinated, defined in this study as 14 days after receipt of dose one through six days after dose two. These findings support CDC’s recommendation that everyone should get both doses of an mRNA COVID-19 vaccine to get the most protection.