Large U.K. study suggests fully vaccinated people are less likely to spread COVID

An almost 100,000-person study out of Imperial College London (ICL) suggests those who are fully vaccinated are three times less likely than the unvaccinated to test positive for COVID-19, and are also less likely to spread the virus to others.

While fully vaccinated people can still occasionally catch COVID-19, "these findings confirm our previous data showing that both doses of a vaccine offer good protection against getting infected," said Professor Paul Elliott, director of the REACT-1 coronavirus monitoring study.

For the study, researchers used random PCR testing to analyze 98,233 individual swabs, 527 of which returned a positive result for COVID-19. Most of the positive samples were of the Delta variant. Based on the data, "researchers estimate that fully vaccinated people in this testing round had between around 50 percent to 60 percent reduced risk of infection, including asymptomatic infection, compared to unvaccinated people," per a press release.

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Last week, the Centers for Disease Control and Prevention implemented updated mask guidance on the grounds that "vaccinated people infected with Delta can transmit the virus," citing an outbreak of roughly 500 people in Massachusetts. The resulting headlines startled many, but the U.K.'s new large study suggests "that fully vaccinated people may be less likely than unvaccinated people to pass the virus on to others," because they have smaller viral loads. This may provide some level of comfort as we learn more about the highly infectious Delta variant now spreading across America.

"We need to better understand how infectious fully vaccinated people who become infected are, as this will help to better predict the situation in the coming months," said Steven Riley, a professor of Infectious Disease Dynamics at ICL, "and our findings are contributing to a more comprehensive picture of this."