London, Mar 26 (IANS): The weakened immune systems of blood cancer patients can improve after they receive a third Covid-19 vaccination, finds a new study.

Patients with lymphoma have defects in their immune system that restrict their response to vaccination. Despite this, the new study found improvements in antibody and T-cell responses after a third vaccine dose, except in patients who had recently received a certain antibody treatment for their cancer.

"Despite the gradual lifting of Covid-19 restrictions worldwide, a cloud continues to hang over immunosuppressed patients, who may not develop protective immune responses after vaccination," said Sean Lim from the University of Southampton, who led the research.

"In particular, individuals with haematological malignancies are at greater risk of severe Covid-19 disease even if they have been vaccinated," Lim added.

For the study, published in the journal Nature Cancer, the team collected blood samples from 457 adult lymphoma patients before they received their first vaccination of either the Oxford-AstraZeneca or BioNTech Pfizer vaccines, and four weeks after the first dose, two to four weeks and six months after the second dose, and four to eight weeks after the third dose.

The study aimed to evaluate the strength of the immune system's response to the vaccines and to help predict how effective the vaccine could be for lymphoma patients.

To achieve this, the scientists measured the ability of antibodies in the blood samples to prevent the viral spike protein from binding to ACE2 proteins, which are the virus's key point of entry into the human body.

They also measured the response of T cells, which form part of the body's immune system, when stimulated by the viral spike.

The results showed that whilst just over half of patients undergoing active cancer treatment had no detectable antibody levels after the second vaccination, T cell responses could be detected in about two-thirds of all patients.

After a third dose, 92 per cent of patients who were not undergoing anti-CD20 treatment for their cancer showed improved antibody responses, compared to 17 per cent who were receiving that treatment.