Vaccinated People Who Get COVID Have These 3 Things in Common, Study Shows

Breakthrough COVID infections share these commonalities, according to new research.

Vaccinations have helped more than 155 million people in the U.S. fight off COVID—but no vaccine is 100 percent effective in preventing the virus from entering your body and, in some cases, making you sick. The Centers for Disease Control and Prevention (CDC) reported that, by the end of April, more than 10,000 people in the U.S. had tested positively for COVID after vaccination, and researchers are still trying to find out more about what these breakthrough cases mean for those affected. One new study concluded that vaccinated people who do get COVID share some key similarities.

RELATED: The CDC Says This One Thing Is Most Likely to Cause COVID After Vaccination.

Researchers from the University of Arizona Health Sciences looked at data for nearly 4,000 participants to find out more about how the vaccine affects people who still get COVID. According to the study, which was published June 30 in the New England Journal of Medicine, 204 of the participants got infected with COVID, with five of them being fully vaccinated and 11 being partially vaccinated. There were also 156 unvaccinated participants. Vaccination status for 32 participants was not determined, so they were excluded from the study.

The researchers found that the few participants who did get infected with COVID after vaccination had three things in common: They were likely to have a lower viral load, experience a shorter infection time, and have milder symptoms than those infected who were unvaccinated.

Per the study, infected participants partially or fully vaccinated with Pfizer or Moderna vaccines had 40 percent less of a viral load than those who were not vaccinated. Early COVID research has suggested that viral load plays a part in how severe one's disease is. An Oct. 2020 study published in Nature concluded that higher viral loads are associated with both increased COVID severity and morality.

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The researchers for the more recent study also found that while a majority of the infections in unvaccinated participants were detected for two or more weeks, individuals at least partially vaccinated were 66 percent less likely to have a confirmed infection that lasted more than one week. Based on the study findings, vaccinated participants were sick with COVID symptoms for about six fewer days than unvaccinated participants. And partial or full vaccination also made participants 58 percent less likely to have a fever associated with their COVID infection.

"If you get vaccinated, about 90 percent of the time you're not going to get COVID-19. Even if you do get it, there will be less of the virus in you and your illness is likely to be much milder," study co-author Jeff Burgess, MD, a professor at the Mel and Enid Zuckerman College of Public Health, said in a statement.

The researchers concluded that two doses of an mRNA COVID vaccine is 91 percent effective against COVID infection, and a single dose is 81 percent effective. "We are still seeing the same high levels of vaccine effectiveness, so we feel good about that," Burgess said. "But more importantly, we've added a number of measures of the severity of infection among individuals who have been vaccinated as a comparison to those who haven't, and we measured how much virus there is and for how long."

RELATED: 3 in 4 Fully Vaccinated People Who Get Severe COVID Have This in Common.

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