85 Percent of Breakthrough COVID Cases Now Have This in Common, Study Says

A new study has found a similarity among a majority of vaccinated people who get infected.

From major celebrities like Melissa Joan Hart and Hilary Duff to multiple U.S. senators, breakthrough COVID infections are affecting a wide range of people across the country. Since no vaccine is 100 percent effective, the Centers for Disease Control and Prevention (CDC) says these breakthrough cases are to be expected. But they're increasing as the Delta variant continues to surge, signaling a need for more research about why certain people get the virus after vaccination, and what their cases look like.

RELATED: If You Got Pfizer, This Is When You're More Likely to Get Breakthrough COVID.

There have been at least 193,204 breakthrough cases counted by U.S. states between Jan. 1 and early August, according to The Wall Street Journal. The news outlet says this is probably an undercount for the true number of vaccinated people who have gotten COVID, as people with asymptomatic infections are not likely to get tested for the virus. But when looking at breakthrough cases more closely, new research has found that vaccinated people are more likely to have symptoms than not.

Dutch researchers from Rotterdam's Erasmus Medical Center studied 161 breakthrough infections among a group of more than 24,000 vaccinated health care workers between April and July. According to their findings, which were preprinted Aug. 21 on medRxiv, nearly 85 percent of the breakthrough infections were symptomatic. Only 13 percent of the cases were asymptomatic, while 2 percent were undetermined. But even among those with symptoms, none of these infections required hospital admission, indicating that the vaccines are still protecting people from severe cases.

An earlier Israeli study from July published in the New England Journal of Medicine found that only 67 percent of vaccinated people who got COVID had symptoms. It's worth nothing, however, that the breakthrough infections in the Israeli study were primarily caused by the Alpha variant, as opposed to the infections in the Dutch study, which were largely a result of the highly infectious Delta variant.

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The Dutch researchers concluded that infectious virus particles were found in only around 68 percent of the breakthrough cases, but in nearly 85 percent of cases among unvaccinated people. These results suggest that fully vaccinated people with the Delta variant are less infectious than unvaccinated people, though still capable of infecting others.

The researchers also found that vaccinated people with the new variant got rid of the virus faster than unvaccinated people, even when the unvaccinated people caught a less infectious strain.

"Despite the reduced viral viability, the infectivity of individuals with breakthrough infections should not be neglected," the Dutch researchers stated. In the U.S., the CDC has recommended that vaccinated individuals mask up once again indoors when in areas with significant COVID spread, due to the fact that they can still transmit the virus.

RELATED: 74 Percent of Vaccinated People Who Get Severe COVID Have This in Common.

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