Two studies suggest that "breakthrough" COVID-19 infections may offer improved immune protection against multiple COVID-19 variants, Nature reported.
"Breakthrough" infections is the term for infections which occur after a person has been vaccinated against the virus.
According to Nature, the data from one of the studies indicates that such infections may also protect against Omicron.
Previous studies have shown that those who recover from COVID-19 and then receive a vaccination tend to produce high levels of antibodies against the virus' spike protein, blocking a variety of COVID-19 variants. These individuals' serum tends to block variants more effectively than that of vaccinated people who were never infected and those who have "natural" immunity resulting from infection alone.
What was not clear until now is whether this improved immunity was also generated in individuals who were vaccinated and then experienced breakthrough infections.
In their study, microbiologist Fikadu Tafesse of Oregon Health & Science University in Portland and his colleagues analysed serum from three groups of healthcare workers: those who had had breakthrough infections, those who were infected and then vaccinated, and those who were vaccinated with no history of infection.
They found that in both of the first two groups, the antibody levels were higher than those in the group who were only protected by vaccines. Sera from infected individuals was also "highly effective" at protecting cells from several variants, including Alpha, Beta, and Delta.
The team, which reported their work in Science Immunology, has not yet examined the protection against Omicron.
A second study, published in Cell, was led by structural biologists Alexandra Walls and David Veesler, both at the University of Washington in Seattle.
That team examined those who were infected and then received two doses of a COVID-19 vaccine, alongside those who had experienced breakthrough infections after receiving two doses of the vaccine, and those who were not infected but received three doses of the vaccine.
In all three groups, serum antibody levels blocking variants including Omicron were higher and lasted longer than those of individuals who had been vaccinated only twice and not infected, Nature noted.
The researchers therefore suggested that the number of exposures to COVID-19, via vaccination or infection, is likely a key factor in the quality of a person's immune response. Those who had four exposures - during a 2020 infection and via three separate vaccinations, has "especially strong" antibody responses to several variants, as well as to the original SARS virus.
"Those individuals are clearly doing the best," Veesler said.