Experts say that while three doses of a Covid stroke help protect individuals from serious consequences if they take Omicron, previous infections can affect their immune response. “If you became infected during the first wave, then you can not boost your immune response if you have an Omicron infection,” said Rosemary Boyton, professor at Imperial College London, co-author of the study. The team also found that an infection from Omicron offered minimal additional protection against re-sticking the variant. “When Omicron started flying all over the country, people kept saying it was okay, that would improve people’s immunity,” Boyton said. “What we are saying is that it is not a good immune booster.” The team said the findings could help explain why Omicron re-infections in such a short period of time were so common, adding that the findings were also important for the development of vaccines. Writing in the journal Science, the researchers reported how they tracked the vaccination and infection experiences of 731 triple-vaccinated health workers in the UK from March 2020 to January 2022. The team then used blood samples collected from participants weeks after the third dose of vaccine to investigate their antibody and T-cell responses to the Omicron variant, BA.1. Participants differed significantly in their Covid history, including whether they had a previous Covid infection and, if so, the variant involved. The results showed that, regardless of the participants’ previous history of infection, a few weeks after their third Covid vaccine their T-cell levels were low on Omicron proteins, and antibody levels on Omicron proteins were lower than in other variants. But previous infections also mattered. Among other findings, the team reported that infection with Omicron increased protection against future infection with other variants. However, it offered only a limited boost to protection against another Omicron infection – a response that actually weakened those who also had the original strain of the virus in the past. The team said the results were maintained for both antibody responses and T-cell responses, and suggested that those who stuck Covid in the first wave of the pandemic did not boost their immune response if they then stuck Omicron. The researchers said the finding was a surprise, as it was usually assumed that a previous infection, even of a different variant, would boost a person’s immune response. Professor Danny Altmann, another author of the study, said that while Covid variants such as Omicron had previously been thought to have developed mutations in the spike protein that helped them avoid immune responses, the situation was more complicated. “It’s actually worse than that, because the adjustments have increased [protein] has now actually caused some sort of regulation or disruption of the immune response, ”he said, adding that while the study looked at responses to BA.1, similar findings were possible for other Omicron variants. The team added that with people in the UK having very different histories of Covid infections and vaccinations, the study was significant as it suggested that this “immunological imprint” would shape the subsequent immunity to the next variant. Altman said that while continued low levels of hospitalization and death from Covid in the UK, despite high levels of infection, suggest that Covid vaccines continue to provide protection against death and serious illness, the findings may be important for development of new vaccines. But he added that the findings raise other concerns. “We are not gaining herd immunity, we are not creating protective immunity in Omicron,” he said. “This is how we deal with not getting to the other side of infections and re-infections and pioneering infections.”
