Fully vaccinated people with a past COVID-19 infection may be last to get booster shots.
COVID-19 infection can trigger the immune response in a similar way to booster shots.
Therefore, these people have already had "three exposures," one expert said.
Fully vaccinated people who previously had COVID-19 could be the last in line for boosters, experts say.
Fully vaccinated Americans with the highest risk of severe COVID-19 are eligible for an extra shot to boost immunity against the highly infectious Delta variant, which has mutations that help it avoid the immune response.
Immunity from COVID-19 vaccines starts to wane after about five months, according to real-world data, so eventually most people will likely need an extra dose.
But Dr. Akiko Iwasaki, immunologist at Yale University, told The Wall Street Journal that people who had been fully vaccinated and have previously caught the virus were "likely to be the last group that really needs the booster" because their immune system had had "three exposures" - two vaccine doses and one infection, all of which trigger an immune response.
Dr. Paul Offit, director of the Vaccine Education Center at Children's Hospital of Philadelphia, said that people who were infected and vaccinated "just won the game," per The Journal.
"I wouldn't ask them to get a booster dose. I think they just got it," he said, referring to the immune system boost from an infection. Offit, who is a member of the Food and Drug Administration's advisory panel on vaccines, supports boosters for older adults but not for the general public at this time, The Journal reported.
Gary McClean, professor in molecular immunology at London Metropolitan University, told Insider that, theoretically, vaccinated people who previously had COVID-19 may not need a booster at all.
Vaccines produce an immune response to one part of the virus, called the spike protein, so you get "spike-specific" immunity, McClean said. Getting COVID-19 triggers an immune response to more than one part of the virus, which means your immune system should later be better prepared to fight variants that have mutations, he said.
But McClean also warned it would be "dangerous" for anybody to deliberately try to catch COVID-19 because of the risk of severe disease. Boosters are "generally safe" if given months after vaccination, he added.
Determining who needs a booster
Emerging evidence suggests that people who caught COVID-19 and were then fully vaccinated have the strongest antibody response of any group - stronger than people who have only been infected, or only been fully vaccinated, for example.
Paul Bieniasz, virologist at the Rockefeller University, said that catching COVID-19 after vaccination may not have the same effect. "It's more variable," Bieniasz told Insider.
In the future, we may need antibody tests to determine who needs extra vaccine doses, Bieniasz said.
We can't yet reliably detect whether people have had an antibody response to COVID-19 either before or after vaccination. Protection also wanes over time, so the timing of an infection or vaccination matters too - people who had COVID-19 prior to vaccination may eventually need a booster.