A single dose of a coronavirus vaccine triggers an immune response in around 70% of patients with the blood and bone marrow cancer, myeloma, according to a new study.
Researchers say the findings suggest the jab could provide protection against the virus.
Experts tested for Covid-19 coronavirus antibodies in 93 people with myeloma.
A recent report with a smaller number of patients with the cancer suggested that blood cancer patients might receive limited protection after vaccination.
Myeloma is a cancer of the immune cells produced in the bone marrow, and puts patients at greater risk of severe Covid-19 infection.
There were concerns it could also cause patients to have less protection in response to any vaccine.
In the study published in The Lancet Haematology, researchers tested the blood of patients who had received a first dose of vaccine.
They found that 56% of the myeloma patients (52 of 93) tested positive for the coronavirus IgG antibodies.
The researchers further analysed the blood of 40 of the patients who tested negative to see if they had other types of antibody indicating some immune protection against Covid-19.
They found an additional 13 patients had some anti-Sars-CoV-2 antibodies.
According to the paper, around 70% of the patients with myeloma tested therefore had an immune response to the vaccine.
The study, led by The Institute of Cancer Research, London (ICR), and The Royal Marsden NHS Foundation Trust, aimed to find out whether vaccine protocols needed to change for this group of cancer patients.
The patients in the study had either received the AstraZeneca or Pfizer vaccine and been given a first dose at least three weeks before their antibody blood test.
Researchers found no significant difference in the percentage of patients with a positive antibody result between those who received the Pfizer (26/48, 54%) and AstraZeneca (26/45, 58%) vaccines.
They say this supports the current guidance for people with myeloma to accept whichever vaccine is offered to them.
A patient’s age, sex, white blood cell level, or time since vaccination, had no impact on their immunity, the study indicates.
The main difference between people with myeloma was based on how they were responding to cancer treatment, 66% of those responding well to treatment showed immunity compared with only 30% of patients responding poorly to treatment.
However, the researchers stress that the results do not tell us for certain that the vaccines protect patients with myeloma against Covid-19.
But they have been able to use the information to provide some reassurance to patients who were concerned that vaccines would not work at all.
Researchers also found an association between poor immune response to the vaccine and patients being immunosuppressed or being on treatment at the time of vaccination.
However, given that pausing of treatment carries its own risk, the authors say decisions around the possible pausing of treatment should be made on an individual basis.
The immune response might improve after a second dose of the vaccine and the ICR and Royal Marsden clinicians are continuing to test antibody status after patients have had a second jab.
Study co-leader Dr Kevin Boyd, consultant haematologist at The Royal Marsden NHS Foundation Trust and leader of the Myeloma Diagnostics and Novel Treatments team at the ICR, said: “Patients living with myeloma have had a difficult time during the coronavirus pandemic with long periods of enforced shielding.
“Because they are a vulnerable group, they were prioritised in the vaccination programme, along with many other patients with blood cancers.”
He added: “This study is not reassuring for every patient, as we do see reduced vaccine response rates compared with the general population.
“However, overall the results are encouraging, showing that the majority of patients do respond to their first vaccine dose, and I expect this to improve following the second dose.
“As society begins to unlock, our patients wish to start seeing relatives and loved ones again and, like all of us, start to enjoy a more normal life.
“I hope this study provides some reassurance that this should be possible.”