The Omicron variant of coronavirus “poses a greater risk” to people with blood cancer, experts have warned.

Researchers wanted to examine the effect of a booster dose among patients with cancer, including those with blood cancer.

Experts from the Francis Crick Institute and The Royal Marsden NHS Foundation Trust have been tracking the level of antibodies in the blood of cancer patients after vaccination.

Antibodies work as part of the body’s defence system by identifying and attacking viruses, these can be generated through vaccination or can occur naturally after someone has had an infection.

The team measured levels of antibodies which specifically block the Omicron variant from infecting cells, also known as neutralising antibodies.

Patients with solid tumours appeared to generate antibody responses similar to people without cancer.

But among patients with blood cancer who had three doses of a Covid-19 vaccine, only 56% generated neutralising antibodies, according to the study which has been highlighted in correspondence published in The Lancet.

This means that after three doses of vaccine 44% of patients with blood cancer did not generate these neutralising antibodies.

The researchers highlight that antibodies are not the only line of defence in the body and patients may also have protection from other parts of the immune system.

But they said that the study backs the need for four jabs for this immunocompromised group of people.

“We found that a third vaccine dose boosted the neutralising response against omicron in patients with cancer, but the effect was blunted in patients with blood cancer compared to those with solid cancer,” they wrote.

They said that their study supports the UK policy of offering a fourth jab to some patients.

In the UK, people with severe immunosuppression aged 12 and over are offered three Covid-19 jabs as an initial course of vaccination. They are then offered a fourth booster.

Dr Samra Turajlic, lead author and group leader at the Crick and consultant medical oncologist at The Royal Marsden, said: “The pandemic has been especially difficult for people living with cancer and up-to-date information about immunity levels are particularly important for this vulnerable group.

“We now know that the immune response to vaccines in patients with solid cancers are robust after three doses as compared to people without cancer, even against the new Omicron variant.

“But for people with blood cancers, Omicron poses a greater risk.

“These patients should remain cautious and come forward for their fourth booster dose as soon as it’s available to them.

“Protecting this vulnerable group is important, especially in the light of the recent easing of Covid-19 restrictions in the UK such as ending mandates requiring people to wear a face mask.

“Public health measures must be inclusive and supportive of everyone, including vulnerable people and their carers.”