These groups included people with an Omicron infection who had previously gotten two or three vaccine doses; vaccinated/boosted people who had caught the original virus or the Delta variant; vaccinated/boosted people who hadn’t caught any infection; and unvaccinated people who had freshly caught Omicron.
However, unvaccinated people who were only infected with Omicron did not develop the same type of broad immune response.
But they do line up with past research suggesting that people with hybrid immunity to the coronavirus—the result of being vaccinated and infected, in either order—can promote a broader immune response, particularly when people are infected by different variants.
In contrast, other research has found that unvaccinated people infected with Omicron do not seem to develop durable protection against other variants of the virus.