In rare cases, people fully vaccinated against COVID and immune to the virus can still develop the disease. New findings from Rockefeller University now suggest that these so-called breakthrough cases could be due to the virus’s rapid evolution, and that ongoing tests on people who are immune will be important to help mitigate future outbreaks.
The research, published this week in the New England Journal of Medicine, reports the results of continuous surveillance within the Rockefeller University community, where two fully vaccinated people have tested positive for the coronavirus. Both had received two doses of the Moderna or Pfizer vaccine, with the second dose occurring more than two weeks before the positive test. One person was initially asymptomatic and then developed symptoms typical of COVID-19; the rest developed symptoms before the test. Both individuals recovered at home, a result consistent with evidence suggesting that the vaccination is effective in preventing serious illness.
Genome sequencing revealed multiple mutations in both viral samples, including the E484K variant in one individual, first identified in South Africa and Brazil, and the S477N variant in the other individual, which spreads in New York since November.
“These patients were vaccinated, had good immune responses and nevertheless went through a clinical infection,” explains Robert B. Darnell, professor The Robert and Harriet Heilbrunn, who led the research with immunologist Michel C. Nussenzweig, virologist Paul Bieniasz, and geneticist Richard P. Lifton. Researchers were able to discern a quantifiable amount of virus in saliva samples from ongoing routine testing at Rockefeller and sequence viral RNA using a new coronavirus testing method developed in Darnell’s lab by postdoctoral associate Ezgi Hacisuleyman with assistance from senior research associate Nathalie Blachere. Since January, the university has required all employees working on site to be tested weekly using this saliva-based PCR test.
The observations suggest what is likely a low but persistent risk in vaccinated individuals, and the possibility that they may continue to spread the virus.
“The idea that we could do away with testing in the post-vaccine world entirely is probably not good at the moment; for example, even fully vaccinated people who develop respiratory symptoms should consider getting tested for COVID-19, ”says Darnell. “Conversely, exposure to people with a known infection, even if they are fully vaccinated, should be taken seriously and again, people should consider getting tested.”
“Given the scale of the pandemic, there is currently a huge amount of the virus around the world, which means a huge opportunity for mutations to grow and spread,” he adds. “This is going to be a challenge for vaccine developers over the next few months and years.”
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