New CDC Study Shows mRNA COVID-19 Vaccines are 94% Effective in Health Care Professionals

A new report from the US Centers for Disease Control and Prevention (CDC) found that mRNA vaccines (Pfizer-BioNTech and Moderna) were highly effective in reducing symptomatic COVID-19 infections among health care professionals.

“This report provided the most compelling information to date that COVID-19 vaccines were performing as expected in the real world,” CDC Director Rochelle P. Walensky, MD, MPH, said in an agency press release. “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.”

Researchers analyzed interim data from an ongoing test-negative case-control study covering 500 000 health care professionals across 33 sites in 25 US states. The data for this planned interim report were collected between January-March 2021.

The study compared vaccination status of participants who tested positive for SARS-CoV-2 and had at least 1 COVID-19-like symptom (cases) with vaccination status of those who tested negative (control).

Among the 1843 participants, there were 623 cases and 1220 controls. Vaccine effectiveness estimates were calculated by comparing the odds of COVID-19 vaccination in cases and controls. According to the press release, the large sample size allowed for a precise vaccine effectiveness estimate with narrower confidence intervals than previous CDC findings published March 29, 2021.

Researchers found that symptomatic COVID-19 illness was reduced by 94% (95% confidence interval [CI]=87%-97%) among participants who were fully vaccinated (defined as ≥7 days after receipt of second dose), and by 82% (95% CI=74%-87%) among those who were partially vaccinated (defined as 14 days after the first dose through 6 days after the second dose).

“These interim results demonstrate that complete vaccination with authorized mRNA COVID-19 vaccines is highly effective in preventing symptomatic COVID-19 among HCP, supporting the results of phase III trials and additional accruing evidence in recent observational studies,” authors concluded.