Two reports of so-called coronavirus breakthrough infections — in which fully vaccinated individuals get the illness — suggest that the vaccines still offer strong protection against severe disease even in the face of variants.
The cases, detailed in the New England Journal of Medicine on Wednesday, were in two women out of more than 400 fully vaccinated study participants who were tested for Covid-19 weekly. Both women developed mild cases of the disease and recovered quickly.
The study’s co-author, Dr. Robert Darnell, a professor and senior physician at the Rockefeller University in New York City, said the two cases are not cause for alarm.
“They certainly didn’t need to be hospitalized,” he said. “They had at-home cases of Covid-19.”
As the number of fully vaccinated individuals in the United States increases, so too will reports of breakthrough infections. Last Friday, the Centers for Disease Control and Prevention said it had received reports of around 5,800 breakthrough infections out of more that 77 million fully vaccinated people.
Breakthrough infections can occur because no vaccine is 100 percent effective. Even so, such cases remain very rare.
CDC officials are gathering more data on breakthrough cases to determine if any patterns exist among patients. Among the questions the agency is asking is whether certain variants are more likely to play a role in breakthrough cases.
Both of the cases in the New England Journal of Medicine report were sequenced, and both cases were found to share certain mutations with the variants first identified in the United Kingdom and New York. However, neither contained all the mutations to match these previously identified variants. (Variants of the virus can contain a number of mutations.)
Still, experts cautioned that because the report included just two cases, it’s too early to draw any conclusions about which variants are most likely to lead to breakthrough infections.
One of the samples contained a mutation called E484K, which is also found in the variants from South Africa, Brazil and New York City, and is thought to help the virus evade the body’s immune response, to a degree.
Jeremy Kamil, a virologist at LSU Health Shreveport, said that he wasn’t surprised this mutation was detected, as lab data suggests it would play a role in breakthrough cases.
“If you ask scientists what mutations you’d expect to see in a breakthrough infection, I think the No. 1 answer you’d get would be E484K,” said Kamil, who wasn’t involved with the new study.
Also Wednesday, two studies published in the CDC’s Weekly Morbidity and Mortality Report, touched on breakthrough infections in nursing homes. One report identified 22 breakthrough infections across 78 Chicago-area nursing homes, which had fully vaccinated nearly 15,000 residents and staffers from December through March. In two-thirds of the breakthrough cases, the infections were asymptomatic, though several people developed mild to moderate symptoms, the report said. Two patients were hospitalized and one individual died.
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The second report focused on a Covid-19 outbreak at a Kentucky nursing home in March. Twenty-six residents and 20 staffers tested positive, including 18 residents and four staffers who were fully vaccinated. Sequencing of the cases detected the same E484K mutation seen in the New York cases.
However, those who had been vaccinated were still 87 percent less likely to develop symptoms compared with those who were unvaccinated.
“The results from this study are quite telling that vaccination resulted in decreased likelihood of infection and symptomatic disease in a high-risk population” like a nursing home, said Jason Kindrachuk, an assistant professor of medical microbiology & infectious diseases at the University of Manitoba in Winnipeg.
Similarly, the women described in the New England Journal of Medicine report also had mild symptoms, Kindrachuk, who was not involved with the new reports, said. “The vaccines did exactly what we had assumed based on the clinical trial data and the real world data: they protected from severe disease.”
One of the patients from the New England Journal of Medicine report, a healthy 51-year-old woman, tested positive for Covid-19 on March 10, 19 days after her second dose of the Moderna vaccine. She said she followed guidelines including masking and social distancing, but developed symptoms including a sore throat, congestion and a headache. The day after her test, she lost her sense of smell. All of her symptoms went away a week later.
The second patient, a 65-year-old woman with no risk factors for severe Covid-19, tested positive March 17, 36 days after her second dose of the Pfizer-BioNTech vaccine. She got sick two weeks after her unvaccinated partner was diagnosed with Covid-19.
Her symptoms included fatigue, sinus congestion and a headache. As in the first case, her symptoms went away after just a few days.
While data from the CDC suggest that breakthrough infections are rare, Darnell said that it would be prudent for fully vaccinated people to get tested for Covid-19 if they develop symptoms that resemble the illness.
“If you do get sick after vaccination, and it looks like, smells like, and sounds like Covid-19, it may be Covid-19,” he said.