CDC cites Mayo Clinic research when discussing need for COVID-19 booster shot

The exterior of the Mayo Clinic in Rochester, Minnesota. (FOX 9)

The CDC decision to recommend a third shot was made in part with the results of new research from Mayo Clinic.

While the results still need to be peer-reviewed, the CDC cited the pre-print results along with other research that shows the Moderna and Pfizer shots become less effective over time.

Mayo looked at 25,000 vaccinated and unvaccinated Minnesotans from January through July. When they broke out the data for the month of July alone they found both the Moderna and Pfizer vaccines were very effective in preventing hospitalizations.

However, when the Mayo researchers looked at preventing infection, they found the effectiveness dropped. The Moderna shot was 76% effective and the Pfizer shot dropped to 42%.

Important to note these observational results are not a clinical trial. Mayo Dr. Melanie Swift said there are confounding factors.

"There is confounding by the way the vaccines were originally given," said Dr. Swift. "They were rolled out originally to higher risk people, so higher risk people have been vaccinated longer than lower risk people."

That means those higher risk people may be skewing the results. The Mayo Clinic is modeling the infection rates county-by-county. By August 30, Mayo Clinic is predicting fast growth in both cases and the infection rate across Minnesota, especially in counties there the vaccination uptake is low. In southeast Minnesota, Dr. Swift says they are already seeing the impact of the delta variant.

"I can say that here in Rochester we have seen a significant rise in the hospital census of COVID patients," said Dr. Swift. "We are not at a level where we were seeing COVID admissions last fall during the surge, but certainly a significant increase since August."

Based upon their modeling, Mayo is preparing for an even higher hospital census in the coming weeks.