Covid-19 vaccines continue to offer strong protection against serious illness and hospitalization, according to research of more than one million people published Wednesday in The Lancet Infectious Diseases.
The findings come as the United States prepares to begin offering booster shots to all Americans later this month – a move driven in part by data according to federal officials indicates the ability of vaccines to dampen infections could decline.
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But protection against the most severe forms of the disease seems to be maintained.
The new research shows that vaccines keep people out of the hospital and intensive care unit and prevent deaths, said Dr. Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, who was not involved in the study.
That is “the goal of these vaccines,” he said, adding that the results apply to “people of all ages and co-morbidities” even amid the spread of the highly contagious delta variant.
In the Lancet study, researchers from the UK analyzed data from a project called the ZOE Covid Study, where users report symptoms, immunization status and other demographic information daily through an app.
Researchers looked at data collected on more than one million people from December 2020 to July 2021, a period that covered both alpha and delta variant waves in the UK. Participants received two doses of Pfizer-BioNTech, Moderna or AstraZeneca vaccine.
Overall, less than 0.2% of participants reported a breakthrough infection, with such cases being more likely in people already considered vulnerable, including the elderly or those with underlying illnesses.
When breakthrough infections did occur, most were mild – only 6% of people with breakthrough infections reported symptoms. In addition, vaccination has been shown to reduce the risk of hospitalization by more than two-thirds.
Two other studies published Wednesday also found an extremely low rate of breakthrough infections.
The first, published in the JAMA Network Open, analyzed infections among more than 5,300 vaccinated health workers in Israel. Only 27 of these infections were found. No deaths were reported and only one patient required hospitalization. The study, however, was completed before the delta variant became the dominant strain in Israel.
The other, published in the New England Journal of Medicine, detected 94 peak symptomatic infections in more than 16,000 health workers. This study, which ran through July, found that breakthroughs increased as the delta variant became dominant.
“Like a watchdog”
Since the Covid-19 vaccines were deployed at the end of 2020, researchers have been monitoring breakthrough infections meticulously.
This breakthrough in infections doesn’t mean vaccines don’t work. On the contrary, experts say, revolutionary infections were always expected, because no vaccine is 100% effective.
“Vaccines are like a watchdog,” said Dr. Rachel Presti, an infectious disease physician at Washington University in St. Louis. A guard dog will prevent most break-ins, but it’s possible that a thief will still manage to sneak in.
The first results of the Phase 3 clinical trial of the first two vaccines authorized in the United States set the bar incredibly high, with Pfizer-BioNTech reporting 95% efficacy and Moderna 94% efficacy against symptomatic diseases.
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This huge success may have inadvertently led to unrealistic expectations of vaccines, said Dr Abinash Virk, infectious disease specialist at the Mayo Clinic in Rochester, Minnesota.
“I think people in general thought, ‘I got the vaccine, I should never get an infection. I should be 100 percent protected, ”Virk said.
The measles, mumps and rubella vaccine is considered the most effective vaccine available, preventing 97 percent of measles cases.
But part of the reason this vaccine works so well is that the measles virus is no longer circulating widely, so there is much less chance for a vaccinated individual to be exposed and an even lower chance of a. revolutionary infection.
“Vaccines work best when there is less virus circulating,” Presti said.
According to data from the Centers for Disease Control and Prevention, community transmission is currently considered high in 94% of US counties.
Studies from the JAMA Network Open and the New England Journal of Medicine also found that breakthrough infections were more often contracted at home, despite health workers spending their days around Covid cases in hospitals.
“When we work in the hospital, we are very aware of the exposure,” said Virk. “We let our guard down when we are at home.”
That people are more susceptible when they’re not wearing masks or moving away physically isn’t surprising, Virk said, and it shouldn’t be disheartening either. On the contrary, it shows that adding layers of protection can improve the potency of vaccines.
“What we hear more and more is that [vaccinated health care workers] become infected after their children, aged 12 or younger, are infected, ”said Dr. Francesca Torriani, infectious disease specialist at UC San Diego Health and lead author of the study in the New England Journal of Medicine.
“The good news,” she said, “is that these infections are still very mild.”
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