Patients with cancer who receive chemotherapy and some targeted therapies may mount an inadequate immune response to COVID-19 vaccination, according to a study.

Researchers at Mayo Clinic Cancer Center have found that targeted therapies, such as CDK4/6 inhibitors and therapies targeted at B cells, also may cut COVID vaccine response. "It is important for patients with cancer who are receiving chemotherapy to receive a COVID-19 vaccine," said Saranya Chumsri, a Mayo Clinic haematologist and oncologist, and author of the paper.

Chumsri noted that this advice also applies to patients with cancer who are taking CDK 4/6 inhibitors. These inhibitors are a newer class of medicines used to treat hormone-receptor-positive and HER2-negative breast cancers. While CDK 4/6 inhibitors are not conventionally considered to be as immunosuppressive as chemotherapy, Chumsri found that patients with breast cancer who take these drugs exhibited less optimal neutralising antibody activity.

The study recommends that antibody levels be tested in these patients after vaccination, and they should consider receiving booster vaccinations for COVID-19. The findings are published in Mayo Clinic Proceedings: Innovation, Quality, and Outcomes.

About 2 per cent of the global population is considered at increased risk of an inadequate response to a COVID-19 vaccine. This includes people with blood cancers or other cancers being treated with chemotherapy, patients on dialysis, those taking medications after an organ transplant or who are taking immunosuppressive drugs for conditions including multiple sclerosis and rheumatoid arthritis.

A real-world retrospective study led by US drugmaker Pfizer, involving nearly 1.2 million people, showed COVID-19 infections in the 'fully' vaccinated are rare but are more common and severe in people with weaker immune systems, which includes cancer patients.

In another study, published recently in the journal Annals of Oncology, fully vaccinated patients with cancer who had breakthrough COVID-19 infections remain at high risk for hospitalisation and death. The World Health Organisation (WHO), in October, recommended that people with weakened immune systems should receive an additional dose of a COVID-19 vaccine, due to their higher risk of breakthrough infections after standard vaccination.