And when outbreaks do occur, vaccines always offer good protection. A second CDC study looked at an outbreak at a Kentucky nursing home where only half of the staff were fully immunized. The outbreak, which started with an unvaccinated staff member, resulted in 46 covid-19 infections. Of 71 residents vaccinated, 18 (25%) were infected, two were hospitalized and one died. The staff behaved better. Of the 56 employees vaccinated, four (7%) were infected. Most of these infections were asymptomatic. Only 6.3% of vaccinated residents and staff developed symptoms, compared to 32% of unvaccinated people.
During an outbreak in a nursing home, “staff and residents are constantly confronted with the pathogen of SARS-CoV-2,” says Meagan Fitzpatrick, who models infectious diseases at the University of Medicine School of Medicine. Maryland. It is therefore encouraging to see such a small number of infections in this type of situation.
New studies also suggest that variants may be behind some of these breakthrough infections. Viral variants are “one of the wild cards,” said Anthony Fauci, chief medical adviser to the President of the United States, in a report. Report April 12. Although there is little actual data, laboratory studies suggest that at least some of the variants are less susceptible to vaccine-induced antibodies than the original SARS-CoV-2.
In the Kentucky study, researchers found that the outbreak was fueled by a variant known as R1, which had not previously been identified in the state. This virus had several important mutations which had also been identified in other variants. For example, the E484K mutation, also found in the B.1.351 variant first identified in South Africa, appears to help the virus escape the antibody response. And the D614G mutation could increase transmissibility. The authors note that although vaccination reduces the likelihood of infection and symptomatic illness, the virus still manages to infect more than a quarter of vaccinated residents and about 7% of staff. This suggests that the vaccine might not work as well against this variant, but the authors warn the study was small. (The Chicago study authors did not sequence the virus.)
A study from the New England Journal of Medicine monitoring infections among staff at Rockefeller University in New York. Between January 21 and March 17, researchers tested 417 employees who had received a full course of the Pfizer or Moderna vaccine. Two women tested positive. When the researchers sequenced the viruses, they found that each was a slightly different variant, and that the viruses did not exactly match those that had been previously identified.
One woman, for example, had a variant with mutations found in B.1.1.7, which originated from the UK, as well as mutations common to B.1.526, which originated from New York. “She had variants somewhere in between,” says Robert Darnell, Rockefeller physician and biochemist and lead author of the study.
When a rupture infection occurs, it is assumed that the patient has failed to develop a strong immune response to the vaccine, Darnell says. But that didn’t seem to be the case with this woman. Darnell managed to get a blood sample shortly after testing positive. He and his colleagues found high levels of antibodies capable of neutralizing SARS-CoV-2. Because she was newly infected, the antibody response was likely due to the vaccination, not her recent infection. Antibodies take a long time to develop.
It’s not entirely clear why her immune system failed to protect her from infections, but one possibility is that the variant managed to avoid her response. “For this particular patient, it’s probably the best explanation for what we’ve seen,” says Stephen Kissler, epidemiologist at the TH Chan School of Public Health at Harvard. “It’s no surprise to me that a lot of these breakthrough infections we’re seeing come from variants,” he adds. As more and more people get vaccinated, “there is an evolutionary selection pressure that is applied.”
On the other hand, as more and more people get vaccinated, we will see fewer infections and the virus will have less opportunity to mutate. And Fitzpatrick points out that while immune leakage explains the woman’s infection, this is only one case. And there is no evidence that she passed the infection on to other people who had also been vaccinated. The phenomenon deserves further study, but “I don’t see it as alarming yet,” she said. “There is not yet a public health crisis.”
And even when rupture infections do occur, it doesn’t necessarily mean the vaccine has failed, says Monica Gandhi, an infectious disease physician at the University of California, San Francisco. Antibodies are only part of the immune response. T cells also play a huge role, strengthening other parts of the immune system and killing off the virus once it enters the body. They do not prevent infection, but they can stop the spread of the virus. And some research suggests that the body’s T cell response will be much harder to evade. “You can actually get a mild infection, but I hope you will still be protected against serious illness,” Gandhi says.
Nonetheless, it is important to follow breakthrough infections to look for unexpected changes. A growing number of infections in people vaccinated could mean a decrease in immunity or the emergence of a new variant that can bypass the immune response. Vaccines may need to be changed and we may need booster shots. But over time, “our bodies will develop a more complete immune response,” says Kissler. “And even if we are re-infected, we will be protected from the most serious consequences. In the long term, the outlook is good. ”