Covid vaccinations may not be enough to protect immunocompromised people from infection even when they have generated antibodies, researchers have found.
It will mean regular boosters for the vulnerable groups to reduce the risk of severe infection, the team from Cambridge University concluded.
While most immunocompromised individuals have received three or more doses of the Covid-19 vaccine, they still account for more than a fifth of hospitalisations, admissions to intensive care units, and overall deaths.
Now a study in 197 patients with vasculitis who were taking ritixumab and who had been vaccinated with the Astra Zeneca-Oxford or Pfizer vaccine showed that although vaccination induced seroconversion, this in itself was not always sufficient to neutralise the virus.
Writing in Science Advances, the team said every immunocompromised individual they looked at required at least three doses of the vaccine to protect them across a range of variants up to and include Omicron.
It builds on research done in the pandemic, which showed that immunocompromised people were particularly vulnerable to Covid-19 and struggled to clear the infection giving the virus more opportunities to mutate.
These patients were in a particularly at-risk category because rituximab depletes the number of B-cells in the body, but these are the immune cells responsible for producing antibodies.
The researchers concluded that results have ‘significant implications’ for individuals treated with rituximab in the post-Omicron era, underpinning the need for ongoing boosters in clinically vulnerable populations to provide ongoing protection.
It also highlights an ‘urgent need’ for additional strategies to boost vaccine-induced immunity in these groups ‘as well as preferential access for such patients to updated vaccines using spike from now circulating Omicron lineages’, they concluded.
Researcher Kimia Kamelian, a Gates Cambridge scholar, said: ‘We know that immunocompromised individuals are particularly vulnerable to diseases such as Covid-19 because their immune systems struggle to clear infections.
‘Vaccinations offer some protection, but our study shows that only repeated vaccinations – often four or more – offer the necessary protection.’
In November, the Joint Committee on Vaccination and Immunisation announced a narrower cohort of patients would be eligible for Covid vaccination from this autumn.
Both the spring and autumn Covid vaccine campaigns in 2025 should be restricted to the over-75s, residents of a care home for older adults and those six months and over who are immunosuppressed, they recommended.
Ministers will make the final decision on eligibility but have accepted the advice for the spring booster campaign.
Professor Ravi Gupta, professor of clinical biology at the Cambridge Institute of Therapeutic Immunology and Infectious Disease, added: ‘This of course has implications for the individual, who is more likely to have prolonged infection and a much greater risk of severe infection, but it also gives the virus multiple opportunities to mutate.
‘We know from our previous work that at least some of the variants of concern probably emerged during chronic infections. That’s why these individuals must be given priority for updated vaccines against new variants.’
