By Michelle Roberts Health editor, BBC News online
Some patients with impaired immune systems have a low or absent antibody response after receiving two doses of Covid vaccine, a UK study has found.
Experts do not yet know what that means for protection, but say booster shots are probably a good idea for certain immunosuppressed people.
It includes those with vasculitis who are taking a strong anti-inflammatory medicine called rituximab.
Some other countries have already started giving out booster Covid doses.
The UK is expected to begin offering vulnerable groups a booster shot next month, but is waiting for recommendations from an independent advisory body called the JCVI.
The Octave study, funded by the Medical Research Council and coordinated by experts at the University of Birmingham, is part of the evidence that will help inform the JCVI decision.
People enrolled on the trial include patients with cancer, inflammatory arthritis, diseases of the kidney or liver and those who are having a stem cell transplant.
Findings from lab tests on blood samples from 600 of these volunteers, published as a pre-print by The Lancet medical journal, suggest:
But 60% had antibody levels comparable to healthy young people and all of them had optimal levels of another type of immune cell response – T cells – that can clear coronavirus infection from the body.
Recent research using real-world data on Covid illness rates in more than a million at risk people, suggests Covid jabs are very effective for people with underlying health conditions, reduced the risk of symptomatic Covid-19 by around 90%.
Prof Iain McInnes, lead of the Octave trial and from the University of Glasgow, said: “While 40% of these clinically at-risk patent groups were found to have a low or undetectable immune response after a double dose of the vaccine, we are encouraged that this figure isn’t higher.
“However, it is possible even partial protection may be clinically beneficial, and this is something we will closely monitor.”
Prof Eleanor Riley, an expert in immunology and infectious diseases at the University of Edinburgh, said: “As it is T cells that are particularly effective at stopping us getting severely ill and needing hospital treatment, we would expect that the vaccine is still offering substantial protection to most of these highly vulnerable people.”
Prof Charles Swanton from Cancer Research UK said: “We know the results could be worrying for those who are clinically vulnerable, but anyone undergoing cancer treatment should continue to follow the advice of their doctors and we encourage all who can to get the vaccine.
“With restrictions easing, you may wonder if you should be shielding – talk to your doctor, family and friends and ultimately you need to do what’s right for you.”
An extension of the Octave study will now look at the effect of giving patients and booster shot.
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