The Centers for Disease Control and Prevention are looking into 5,800 cases of people who have contracted the COVID-19 virus after they have been fully vaccinated.
The infections, called vaccine breakthrough infections, have been seen in several states, and may point to an increase in the spread of novel coronavirus variants.
“Essentially, these are cases that you see amongst vaccinated individuals during a period in which you expect the vaccines to work,” Dr. Saad Omer, a vaccine researcher at Yale University, told NPR.
While the vaccines have been shown to be highly effective, they are not 100%, Omer said. It is not at all uncommon to see some infections despite immunization, he pointed out.
“So the bottom line is: It’s expected. No need to freak out,” Omer said.
Researchers are still trying to determine how and why the breakthrough infections are occurring, and if there is a common denominator in the cases. According to the CDC, females accounted for 65% of those who reported getting the virus after vaccination.
Nearly a third of the 5,800 cases were infections that produced no symptoms.
“The CDC is monitoring reported cases for clustering by patient demographics, geographic location, time since vaccination, vaccine type or lot number and SARS-CoV-2 lineage,” the agency told CNN.
Natalie Dean, a biostatistician at the University of Florida, agreed that it is not unusual for some who are vaccinated to still get the virus.
“This is what we expect to see: some level of cases among vaccinated people,” Dean told Vox.
“Nothing is 100%,” Dean said, referring to the three vaccines used in the United States. “When you start to talk about vaccinating millions of people, even things that occur relatively infrequently will start to pop up.”
According to clinical trial data, the Pfizer/BioNtech vaccine is 95% effective at preventing COVID-19, while the Moderna vaccine is 94% effective and the Johnson & Johnson vaccine is between 66% and 72% effective (and higher at preventing severe disease). None of the vaccines are 100% effective against the virus.
The number of breakthrough infections depends on the number of people vaccinated, Dean explained. In other words, the more COVID-19 infections in a community, the more likely a breakout infection is to occur.
“The risk of these breakthroughs is really reflecting just how much transmission is in the community,” Dean said.
Dr. Anthony Fauci, who has been a White House adviser on the pandemic since it was declared 13 months ago, says he sees no reason to become concerned over breakthrough cases.
“There’s nothing there yet that’s a red flag,” Fauci said. “We obviously are going to keep an eye on that very, very carefully. But I don’t see anything that changes our concept of the vaccine and its efficacy.”
Of the 5,800 breakthrough cases the CDC is investigating, 74 people have died and 396 people have been hospitalized with the virus. More than 76.6 million Americans have been fully vaccinated against the COVID-19 virus as of Wednesday.
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