A study shows that people who caught Covid during the first wave of the Pandemic don't get a boost to their immune response if they catch Omicron.
While three doses of a Covid jab help to protect individuals against Omicron, previous infections can affect their immune response, according to experts.
Prof Rosemary Boyton is a co-author of the study.
An Omicron infection gave little protection against catching the variant again. Boyton said that when Omicron began flying around the country people kept saying that it would improve their immunity. It isn't a good booster of immunity, that's what we're saying
The findings are important for vaccine development, as they may help to explain why Omicron re-infections have been so frequent.
731 triple vaccine healthcare workers in the UK were followed by the researchers over the course of a year. The team collected blood samples from participants in the weeks after their third dose of vaccine to investigate their responses to the Omicron variant.
The participants had different Covid histories, including whether they had had a previous Covid infection and if so, the variant involved.
The results showed that the participants' levels of T-cells against Omicron were poor a few weeks after their third Covid jab, even though they had previously been exposed to Omicron.
Previous infections were important. Infections with Omicron increased protection against future infections. It only gave a small boost to protection against another Omicron infection, and it was weakened by those who had previously had the original strain of the virus.
Those who caught Covid in the first wave of the Pandemic did not get a boost to their immune response if they caught Omicron, according to the team.
It was thought that a prior infection would boost an individual's immune response.
One of the authors of the study, Prof Danny Altmann, said that the situation was more complex than previously thought, because it had been thought that the Covid variant Omicron had developed mutations that helped them to evade immune responses.
While the study looked at responses to the BA.1, similar findings were likely for other subvariants.
The team said the study was important because it suggested that the different histories of Covid infections in the UK would affect immunity against the next variant.
Despite high levels of infections, Covid jabs continue to offer protection against death and severe disease in the UK, suggesting they could be important for the development of new vaccines.
He said the findings raised other concerns. He said that they are not building up protective immunity to Omicron. We face not being able to come out of infections and re- infections.
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