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Study examines effectiveness of third dose of mRNA COVID vaccines against delta, omicron

The New England Journal of Medicine in April published a study involving researchers at the Rocky Mountain Center for Occupational and Environmental Health (RMCOEH) that examined the effectiveness of a third dose of mRNA COVID-19 vaccines against the delta and omicron coronavirus variants.

It is the second study regarding COVID-19 vaccines that RMCOEH has helped lead to appear in the world’s most prestigious medical journal. “We are thrilled to share the results of this study, which provides valuable information about how the evolution of the coronavirus is affecting one of the key tools in the fight against COVID-19,” said Dr. Sarang K. Yoon, DO, MOH, an assistant professor at RMCOEH and the study’s lead author. “It is gratifying to have the hard work of everyone who contributed to this research acknowledged in the New England Journal of Medicine.”

The study evaluated COVID-19 infections between late August, 2021, and January, 2022, among health care personnel, first responders and other frontline workers who had received a third dose of an mRNA vaccine. The workers had either received three doses from a single manufacturer — Moderna or Pfizer-BioNTech — or a combination of the two vaccines.

Researchers found:

• a third dose was 91% effective in protecting against infection with the delta variant compared to a two-dose protection level of 65%
• a three-dose regimen provided a protection level of 60% against the more transmissible omicron variant, while two doses were 46% effective
• mRNA vaccines continue to provide robust protection against severe outcomes despite omicron’s transmissibility

Dr. Yoon added: “These results show that in this real-world study of workers, the vaccine continues to be effective against the omicron variant of the virus, although at a reduced rate of efficacy compared with the prior delta variant.”

In addition to Yoon, RMCOEH Director Kurt T. Hegmann, MD, MPH, and Matthew S. Thiese, PhD, MSPH, the center’s chief operating officer, were co-authors on the study, which was conducted in collaboration with researchers across the country.

RMCOEH, a program partnership between the University of Utah and Weber State University, has been a leading contributor to research surrounding COVID-19 since the pandemic emerged. In addition to the studies examining the vaccines, the center has conducted research showing COVID-19 likely spreads through aerosols and developed the only occupational health guideline for the disease.

“Researchers across the globe have stepped up over the last two years to address this crisis,” Dr. Yoon said. “We are pleased to have played a role in helping the world understand the disease and the vaccines’ ability to protect against it.”