Should cancer patients receive Covid-19 booster shots? Is it safe to mix Covid-19 vaccines? And when should those on immunosuppressive treatment get vaccinated?

These questions were asked at a virtual forum on Covid-19 vaccination for cancer patients on Saturday (Oct 23).

A panel of six medical experts addressed these and other concerns at the event organised on teleconferencing app Zoom by the College of Clinician Scientists, Academy of Medicine Singapore.

The panellists included College of Physicians Singapore president David Lye, who is also director of the National Centre for Infectious Diseases' Infectious Disease Research and Training Office, and National Cancer Centre Singapore (NCCS) medical director William Hwang.

Here are some of the issues that the panellists discussed.

  1. Should cancer patients get booster shots?

    The panellists urged cancer patients to get vaccinated or receive booster shots due to the high number of cases in the community, adding that studies have shown that the vaccines approved in Singapore are safe for patients receiving chemotherapy and immunotherapy.

    Associate Professor Iain Tan, senior consultant oncologist at NCCS' division of medical oncology, said cancer patients, particularly those on chemotherapy, may be at higher risk of severe complications or death if they are infected with Covid-19.

    Since the start of the pandemic, at least 22 cancer patients in Singapore have died of complications from the coronavirus, 18 of them unvaccinated, he added.

    Responding to concerns raised about vaccine side effects for those on immunotherapy, he said immune-related adverse events are very rare.

    Prof Hwang said: "Booster shots can promote affinity maturation, which causes the antibodies to become better and more targeted."

    Prof Lye noted that side effects from a booster shot would not be worse than those experienced after the first two doses.

    When asked whether cancer patients who have caught Covid-19 should get vaccinated or receive booster jabs, he said: "There is good data from observation of recovered patients and from antibody and immune system studies that a dose of mRNA vaccine after recovery from Covid-19 protects you effectively".
  2. Is it safe/better for cancer patients to mix vaccines for their third shot?

    Prof Lye said a few studies on booster shots from countries such as Britain and Spain have shown that mixing a vaccine that is known to produce fewer antibodies with a vaccine that produces more antibodies will provide more protection.

    Prof Tan added that the antibody response of cancer patients is likely to be weaker than that of the general population.
  3. When can those receiving immunosuppressive treatment such as chemotherapy take their third dose of Covid-19 vaccine?

    Cancer patients should discuss with their oncologists the timing of each dosage because every cancer is different, said the panellists.

    Professor Chng Wee Joo, director of the National University Cancer Institute, said that if patients are considered to be more immunocompromised, they should get a third dose of the vaccine two months after their second dose and a booster shot six months after the third dose.

    This would apply to patients who received either of their two doses while immunosuppressed, are currently receiving immunosuppressive treatment such as chemotherapy or are soon to be immunosuppressed, said Prof Tan.