A healthcare worker administers a dose of the Pfizer-BioNTech Covid-19 vaccine at a vaccination clinic in the Peabody Institute Library in Peabody, Massachusetts, U.S., on Wednesday, Jan. 26, 2022.
Vanessa Leroy | Bloomberg | Getty Images
People who caught Covid-19 before they were vaccinated had a weaker immune response to the shots than those who never had the virus, potentially leaving them less protected against reinfection, new research shows.
Co-funded by the National Institutes of Health, the study released Monday challenges older research that suggested a prior Covid infection enhanced a vaccinated individual’s immune response — a phenomenon known as hybrid immunity, which some scientists believe provides the best protection against reinfection.
In the study, researchers from Stanford University analyzed how immune cells found in the blood called CD4+ T cells and CD8+ T cells respond to Covid infection and vaccination. Those cells work together to produce an immune response that can help fend off the virus, killing other cells that have been infected.
The study found that vaccinating people who had never been infected with Covid before produced “robust” CD4+ and CD8+ T cell responses to the virus. Vaccination in those people also generated cell-signaling molecules that recruit other immune cells to help fight Covid, they said. In contrast, researchers said vaccinating people with prior Covid infections produced “considerably lower” cell responses “with less functionality.”
Unvaccinated people who caught Covid had even lower levels of CD8+ T cells, they added.
The researchers said the findings suggest a Covid infection damages an important immune cell response that is crucial to fighting the virus, which might leave vaccinated individuals with a prior infection less protected.
“The apparent damage of the CD8+ T cell response by viral infection is cause for concern, and may leave even vaccinated individuals with a prior infection at risk for subsequent…
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