People who caught Covid in first wave get ‘no immune boost’ from Omicron

People who caught Covid during the first wave of the pandemic get no boost to their immune response if they subsequently catch Omicron, a study of triple vaccinated people reports.

Experts say that while three doses of a Covid jab help to protect individuals against severe outcomes should they catch Omicron, previous infections can affect their immune response.

"If you were infected during the first wave, then you can't boost your immune response if you have an Omicron infection," said Prof Rosemary Boyton, of Imperial College London, a co-author of the study.

The team also found an Omicron infection offered little extra protection against catching the variant again. "When Omicron started flying around the country, people kept saying that's OK, that will improve people's immunity," said Boyton. "What we're saying is it's not a good booster of immunity."

The team said the findings may help to explain why reinfections with Omicron over a short time period have been so frequent, adding the findings were also important for vaccine development.

Writing in the journal Science, the researchers reported how they followed the vaccination and infection experiences of 731 triple vaccinated healthcare workers in the UK from March 2020 to January 2022. The team then used blood samples collected from participants in the weeks after their third dose of vaccine to explore their antibody and T-cell responses towards the Omicron variant, BA.1.

The participants varied considerably in terms of their Covid history, including whether they had had a previous Covid infection and, if so, the variant involved.