mRNA vaccines significantly reduce severity of Delta, Omicron COVID-19 infections
People who have received two or three doses of an mRNA COVID-19 vaccine are significantly more likely to have milder illnesses if infected with the Delta or Omicron coronavirus variants than those who are unvaccinated, according to a nationwide study involving a team of University of Utah researchers.
The study, which examined healthcare personnel, first responders and other frontline workers in Utah and five other states, builds on previous research that indicates mRNA vaccines provide protection against severe health outcomes associated with COVID-19 despite the variants’ increased transmissibility.
The study was published in the Journal of the American Medical Association (JAMA). It is the latest of several peer-reviewed papers resulting from the nationwide HEROES-RECOVER project funded by the U.S. Centers for Disease Control and Prevention.
Researchers examined 1,199 participants who developed COVID-19 infections. Of the participants, 24% were infected with Delta and 62% contracted Omicron, while 14% had the original virus strain.
Delta highlights:
- Participants who had received two vaccine doses were significantly less likely to be symptomatic than those who were unvaccinated (77.8% vs. 96.1%)
- Symptomatic participants with a third dose were far less likely to experience fever or chills than those who were unvaccinated (38.5% vs. 84.9%) and experienced symptoms for an average of six fewer days (10.2 days vs. 16.4 days)
Omicron highlights:
- The risk of symptomatic infection was similar between participants with two vaccine doses and those who were unvaccinated, while those with three doses experienced a higher risk than the unvaccinated (88.4% vs. 79.4%)
- Symptomatic participants with three doses were significantly less likely to experience fever or chills (51.5% vs 79%) or seek medical care (14.6% vs 24.7%) than the unvaccinated
