Of the 417 employees at Rockefeller University who were fully vaccinated with the Pfizer or Moderna injections, two or about 0.5% later had breakthrough infections, according to the study published Wednesday in the New England Journal of Medicine.
“We have characterized bona fide examples of vaccine breakthroughs as clinical signs,” the researchers wrote in their study. “These observations in no way undermine the importance of the urgent efforts being made at the federal and state levels to vaccinate the US population. Provide greater protection against variants.”
The Rockefeller University researchers found that coronavirus variants with several differences from the original virus caused the breakthrough infections.
One variant that infected one of the patients had the E484K mutation, which was first found in the B.1.351 variant originally identified in South Africa. E484K has been referred to as an “escape mutant” because it has shown that it has the potential to escape some of the antibodies produced by coronavirus vaccines. One of the mutations found in the infections of both study participants included D614G, which emerged early in the pandemic.
One of the breakthrough infections was in a healthy 51-year-old woman who received her second dose of Moderna vaccine on February 19. Nineteen days later, she tested positive for Covid-19 on March 10 after developing symptoms.
The other breakthrough infection was in a healthy 65-year-old woman who received her second dose of the Pfizer vaccine on February 9. She later learned that her partner, who had not been vaccinated, tested positive for Covid-19 on March 3. the following days the woman developed her own symptoms. She tested positive for Covid-19 on March 17.
More research is needed to determine whether similar findings related to breakthrough infections or variants would emerge in a larger group of participants from different parts of the United States.
Experts say some breakthrough cases of Covid-19 are to be expected in people who are fully vaccinated, as no vaccine is 100% effective.
The CDC said breakthrough cases occurred in people of all ages who had been vaccinated, but just over 40% were in people 60 or older. They were also more common in women and 29% were asymptomatic.
The agency said it has developed a national database of Covid-19 breakthroughs for state health departments to report
“Breakthrough vaccine infections make up a small percentage of people who are fully vaccinated. The CDC recommends that all eligible people receive a COVID-19 vaccine as soon as one is available to them,” the CDC said in a statement to CNN.
CNN’s Ben Tinker and Maggie Fox contributed to this report.