The findings, published in the peer-reviewed journal mBio, raise the possibility that vaccine boosters may be equally effective in improving antibodies' ability to target multiple variants of the virus, including the Delta variant, which is now the predominant strain, and the recently detected omicron variant.
While the study was conducted prior to the emergence of Delta and Omicron, Dr. Otto Yang, senior author University of California at Los Angeles (UCLA), said the results could potentially apply to those and other new variants as well.
"The main message from our research is that someone who has had Covid and then gets vaccinated develops not only a boost in antibody amount, but also improved antibody quality - enhancing the ability of antibodies to act against variants," said Yang, Professor of medicine at the David Geffen School of Medicine at UCLA.
"This suggests that having repeated exposures to the spike protein allows the immune system to continue improving the antibodies if someone had Covid then been vaccinated," Yang added.
Yang, however, said it is not yet known whether the same benefits would be realised for people who have repeated vaccinations but who have not contracted Covid-19.
The researchers compared blood antibodies in 15 vaccinated people who had not been previously infected with SARS-CoV-2, with infection-induced antibodies in 10 people who were recently infected with SARS-CoV-2 but not yet vaccinated. Several months later, the 10 participants in the latter group were vaccinated, and the researchers then reanalysed their antibodies.
The results showed that the receptor-binding domain mutations reduced the potency of antibodies acquired both by either natural infection or vaccination alone, to about the same degree in both groups of people.
When previously infected people were vaccinated about a year after natural infection, however, their antibodies' potency was maximised to a point that they recognised all of the Covid-19 variants the scientists tested.
"Overall, our findings raise the possibility that resistance of SARS-CoV-2 variants to antibodies can be overcome by driving further maturation through continued antigenic exposure by vaccination, even if the vaccine does not deliver variant sequences," the researchers write.