MARSHFIELD – A follow-up analysis of the COVID-19 mRNA vaccines showed they continue to be highly effective, and vaccinated people who did get COVID-19 had less detectable virus and were sick for a significantly shorter time with significantly reduced symptoms.

The Centers for Disease Control and Prevention-led study pre-printed in MedRxiv and due for publication in the New England Journal of Medicine on June 30 shows mRNA vaccines to be 91 percent effective after the second dose against SARS-CoV-2, and 81 percent after the first dose. These results follow a CDC report published in March that showed mRNA vaccines to be 90 percent effective after the second dose against SARS-CoV-2, and 80 percent after the first dose.

The study showed the COVID-19 vaccines were highly effective among working-age adults in preventing SARS-CoV-2 infections when administered in real-world conditions, said Jennifer Meece, director of Marshfield Clinic Research Institute’s Integrated Research and Development Laboratory, in a news release. The Research Institute, the research division of Marshfield Clinic Health System, was the sole reference laboratory in the nation to support the studies.

“Study participants also were found to have shed the virus for a shorter duration, had reduced fevers and were sicker for a shorter time,” Meece said. “They also were found to be less likely to spread the virus to others, highlighting how the vaccine continues to improve the health and wellbeing of those being vaccinated and those who are in contact with the vaccinated. In contrast, unvaccinated individuals were sick longer, and shed significantly more virus for longer periods of time, making them a risk to those around them.”

The Research Institute received a $22.5 million CDC grant in July 2020 to play a leading role in a number of COVID-19 studies across the U.S. The Research Institute tested 3,975 samples each week for 17 consecutive weeks from health care personnel, first responders and other frontline and essential workers from across the U.S. The study demonstrated in real world conditions the effectiveness of mRNA vaccines in both symptomatic and asymptomatic COVID-19. 

The Research Institute’s role in the study was testing the specimens, which came from participants who self-swabbed and mailed them to Marshfield. Meece and senior research associates at the Lab, Lynn Ivacic and Elisha Stefanski, were among the authors on these studies. They also assisted by helping analyze the results and write the report.