Recent data from the Centers for Disease Control and Prevention (CDC) shows that the current Delta variant surge—which has seen the national daily case average soar higher than last summer’s highest level—is being fueled largely by infections among unvaccinated people. However, a leaked CDC report also stated that breakthrough infections are still affecting those who’ve received their shots, adding to mounting concerns among some health experts that the virus may be eluding the protection offered by the vaccine. But new research out of the U.K. has shined more light on how likely it is that someone who’s fully vaccinated will catch the Delta variant, offering some good news as cases continue to mount.
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A large study conducted by researchers at Imperial College London, which has not yet been peer-reviewed, used data from over 98,000 swab tests taken between June 24 and July 12. The sample period covers a time when the Delta variant had surpassed the Alpha variant as the dominant strain in the U.K. Results found that people who had received two doses of vaccine were half as likely to test positive for COVID-19 even if they hadn’t shown any signs of symptoms.
The study also found that the vaccines offered even higher effectiveness regarding symptomatic infections, showing a 59 percent efficacy rate for those who had received both shots. And while the findings suggest a significant drop from a previous study conducted by Public Health England that found fully vaccinated people were offered 88 percent protection against the variant, the Imperial College researchers state that the point of their study was to access results from people who may not have been looking to get tested, Reuters reports.
“We’re looking at effectiveness against infection amongst a random sample of the general population, which includes asymptomatic individuals,” Paul Elliot, PhD, an epidemiologist at Imperial College who led the study, said during a press conference. “So again, it’s a different bunch of people,” adding that his study obtained test results from people who may not have chosen to get swabbed otherwise.
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Overall, the study found that three times as many unvaccinated people test positive for the Delta variant, showing a prevalence of 1.21 percent in patients who had yet to receive their shots versus .40 percent prevalence in fully vaccinated patients. The researchers also noted that the viral load measured in vaccinated people was lower than levels in unvaccinated people, meaning they may be less infectious to others.
Ultimately, the researchers concluded that their findings provided some cause for cautious optimism. But they were careful to caution that the Delta variant was still a formidable foe in the fight against the pandemic.
“These findings confirm our previous data showing that both doses of a vaccine offer good protection against getting infected,” Elliot said in a statement. “However we can also see that there is still a risk of infection, as no vaccine is 100 percent effective, and we know that some double vaccinated people can still become ill from the virus. So even with the easing of restrictions, we should still act with caution to help protect one another and curb the rate of infections.”
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