A healthcare worker administers a dose of the Pfizer-BioNTech Covid-19 vaccine at a immunization clinic at the Peabody Institute Library in Peabody, Massachusetts, on Wednesday, January 26, 2022.
Vanessa Leroy | Bloomberg | Getty Images
People who contracted Covid-19 before being vaccinated had a weaker immune response to the vaccines than those who never had the virus, potentially making them less protected from re-infection, new research shows.
The study, co-funded by the National Institutes of Health and published Monday, challenges older research suggesting that previous Covid infection boosted a vaccinated person’s immune response – a phenomenon known as hybrid immunity and by which some scientists believe offers the best protection against reinfection.
In the study, Stanford University researchers analyzed how immune cells found in the blood called CD4+ T cells and CD8+ T cells respond to Covid infection and vaccination. These cells work together to create an immune response that can help fight off the virus and kill other infected cells.
The study found that vaccinating people who had never been infected with Covid elicited “robust” CD4+ and CD8+ T-cell responses to the virus. Vaccination in these people also created cell signaling molecules that recruit other immune cells to help fight Covid, they said. In contrast, the researchers said that vaccinating people with previous Covid infections elicited “significantly lower” cellular responses “with less functionality.”
Unvaccinated people who contracted Covid had even lower CD8+ T cells, they added.
The researchers said the results suggest that Covid infection damages a key immune cell response vital to fighting the virus, which could leave vaccinated people with a previous infection less protected.
“The apparent damage to the CD8+ T-cell response from viral infection is of concern and may put even vaccinated individuals with a prior infection at risk for subsequent infections or other health problems,” the study authors write. They also said the results underscore the need to develop new vaccine strategies that will target boost CD8+ T cell responses in people previously infected with Covid.
dr Stuart Ray, a professor of medicine at Johns Hopkins University, said the study is surprising because it challenges knowledge of hybrid immunity. But he added: “We always have to be careful when something surprises us.”
Ray said the findings could be due to the way the study was designed, pointing in particular to how researchers looked at immune cells in blood rather than tissue.
“The cells in the blood are not an absolute measure of everything in the body. The cells that we know protect us are also in our tissues that fight infection,” he told CNBC. “It’s like looking for something under the lamppost when it’s close over the field. Maybe you don’t see all the cells that are important to us.”
Ray said the study, while interesting, must take into account long-term knowledge of how Covid immunity works: “It’s probably not the last chapter of this story.”
The study comes as researchers continue to study the impact of Covid on individuals even after they have recovered from the virus, which has infected more than 100 million people in the US alone since the pandemic began. The country continues to see nearly 150,000 new cases every week, according to the Centers for Disease Control and Prevention.
The new research also comes as public health officials are considering new approaches to Covid vaccination that could reduce the number of doses people need each year, or require drugmakers to regularly update their shots to catch up to target emerging variants of the virus.
According to the Centers for Disease Control and Prevention, around 81% of the US population is vaccinated with at least one Covid shot, while nearly 70% have completed their primary series doses.