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Vaccine boosters, as well as breakthrough infections after vaccination, provide substantial immunity against COVID-19, according to a new study published in the journal Med.
In particular, the immune response increased significantly against severe disease, even in ages 65 and older, which could signal a shift in the pandemic, the authors wrote.
"Early in the pandemic, we had very high mortality in certain vulnerable groups, such as older adults in nursing homes, but that reality is slowly changing," Marcel Curlin, MD, a co-senior author and associate professor of medicine at Oregon Health & Science University, said in a statement.
"Our study bolsters the idea that vaccination is a pathway to a milder illness," he said. "Even if you're older, your chances of having a severe illness if you're re-infected down the line appear to be much lower than it was at the start of the pandemic."
The research team analyzed blood samples from 99 OHSU employees after vaccination, including some breakthrough cases. They looked at different aspects of the immune response, such as neutralizing antibodies and those that target the spike protein on the coronavirus.
Overall, the researchers found a similar increase in magnitude, potency, and breadth of the immune response among those whose blood was drawn three months after a third booster dose and those whose blood was drawn a month after a breakthrough infection.
The immune response was also strong against the BA.2 Omicron variant, which was circulating at the time of the study. Researchers said they expect an even more robust immune response among people who receive the new bivalent COVID-19 vaccine this fall that targets the BA.4 and BA.5 variants.
"We anticipate that updated vaccine strategies with variant-specific regimens will significantly improve the breadth of the immune response and provide better protections against the SARS-CoV-2 variants," Fikadu Tafesse, a co-senior author and associate professor of molecular microbiology and immunology at OHSU, said in the statement.
In contrast to the beginning of the pandemic, the coronavirus is no longer "novel" to the human immune system, study authors said. Most people in the world have now been vaccinated, infected, or both, which means people have a more effective immune response than before.
Results from this study likely reflect the idea that the virus is evolving to become more transmissible but may be less harmful, Curlin said.
"Boosters and natural infection substantially boost immune responses," study authors concluded. "As the number of Omicron subvariant cases rise and as global vaccination and booster campaigns continue, an increasing proportion of the world's population will acquire potent immune responses that may be protective against future SARS-CoV-2 variants."
Med: "Omicron neutralizing antibody response following booster vaccination compared with breakthrough infection."
Oregon Health & Science University: "New study reveals breakthrough infections increase immunity to COVID-19."
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Cite this: Breakthrough COVID Infections Increase Immunity, Study Says - Medscape - Sep 26, 2022.