Manuela Callari
People with cancer are at a higher risk of developing severe infection when they catch the SARS-CoV-2 virus. That’s because their immune system is weakened by cancer or cancer treatments. But none of the COVID-19 vaccines has been trialled in cancer patients so far. What do we know about their safety and effectiveness?
In Australia, people with cancer (including those who have completed active treatment in the past five years), adult survivors of childhood cancer and their carers are eligible to receive a COVID-19 vaccine as part of phase 1b of the rollout, which began on 22 March.
Many cancer organisations worldwide recommend that cancer patients, including those undergoing therapy, receive their COVID-19 jabs with priority.
The Australian Technical Advisory Group on Immunisation (ATAGI) has given a similar recommendation, but the federal government’s Cancer Australia advises that the decision about whether to be immunised against COVID-19 should be made by the individual patient in consultation with their healthcare team.
“Very few cancer patients were involved in the trials, mostly with the Pfizer vaccine, and not on active chemotherapy,” says Professor Fran Boyle, the president of the Clinical Oncology Society of Australia and a professor of medical oncology at the University of Sydney. She says to date, overseas data have not shown an increase in side effects, but data on efficacy are still very limited.
“Early on, it was quite difficult to know about safety and efficacy,” says Professor Dorothy Keefe, CEO of Cancer Australia. “But now that a huge number of people around the world have had vaccines, it’s very reassuring that there hasn’t been a signal that they are not safe in cancer patients.”
The evidence from cancer patients’ response to other vaccines suggests that, in principle, COVID-19 vaccines place no safety concerns. Boyle says that live virus vaccines are generally avoided in cancer patients, but neither the Pfizer (an mRNA vaccine) nor the AstraZeneca (a non-replicating viral vector vaccine) fall into this category.
Boyle says that people with cancer who have previously experienced an allergic reaction to polysorbate 80 or polyethylene glycol – chemicals found in chemotherapeutics such as docetaxel and paclitaxel – need to speak to their doctors before receiving a COVID-19 vaccine because these chemicals are also found in the AstraZeneca (polysorbate 80) and Pfizer (polyethylene glycol) vaccines.
But the biggest concern at the moment is whether vaccines will offer cancer patients the same level of protection against COVID-19 as they do in the general population. The immune response to vaccination may be reduced in people with cancer, resulting in comparatively lower vaccine effectiveness and protection.
Early results from a study conducted in the UK on the Pfizer vaccine found that cancer patients had lower levels of protection after the first dose of the vaccine, compared to people without cancer. But immune response improved significantly after the second dose.
Evidence from flu vaccinations suggests that people with cancer mount an adequate immune response. However, the level of immunity may depend on the type of cancer, therapies and immune system function. People with blood cancer, for example, generally have a weaker immune system than those with solid tumours, and might need vaccines boosters. “That’s not unheard of. It happens with other vaccines too,” says Keefe.
“Recent transplant, chronic lymphocytic leukaemia, [and] active chemotherapy might all reduce efficacy, but patients should be vaccinated anyway, as should their immediate carers,” says Boyle.
Keefe says people undergoing chemotherapy should consider taking the vaccine one or two weeks after their cancer treatment. Those under hematological malignancy therapies such as bone-marrow transplantation and CAR T-cell therapy might need to wait longer for their immune system to recover. “Each cancer patient on therapy should discuss with their oncologist,” she says.
Several studies are now underway to investigate the immune response to COVID-19 vaccines in people with cancer. But until we have more data available, practising good hygiene and maintaining physical distancing are essential habits to cultivate even after receiving a vaccine.
“Until a sufficiently large proportion of the community is vaccinated, cancer patients should take care after vaccination because it’s difficult for a person to know whether the vaccine has worked in them,” says Keefe. “But vaccines help reduce the severity of the infection, which is why it’s really important that cancer patients get it.”