The world cheered last year when several COVID-19 shots were found to be highly effective in clinical trials. But, given that cancer patients were excluded from the studies, questions swirled over how well the shots would work in that group, especially for those on immunosuppressants.
Now, a set of studies released at the European Society for Medical Oncology (ESMO) 2021 virtual congress are painting a clearer picture: The vaccines—particularly Pfizer’s BioNTech-partnered two-jab Comirnaty—are effective and safe for cancer patients, although some may benefit from an additional booster dose.
In one multicenter study from the U.S. Veterans Affairs (VA) healthcare system, researchers included vaccinated and unvaccinated cancer patients both on and off active therapy.
It’s thought that those treatments, such as chemotherapy and radiation, could impact the immune system and make the vaccines less effective, although the jabs are likely safe, according to the American Cancer Society. Just last month, the FDA approved an additional, or third, mRNA dose for those with weakened immune systems, which includes cancer patients using the immune-tampering therapies.
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In the VA study, veterans with a solid or hematologic malignancy who received systemic cancer-directed therapy at least once since late 2010 were examined. The trial included an equal 29,152 vaccinated and unvaccinated patients in each arm.
With a median follow-up of 47 days, overall vaccine efficacy was 58% two weeks following the second dose, according to the study. Specifically, patients who were on chemotherapy within the three months prior to their first dose showed a 57% efficacy. That figure shot up to 75% for those off systemic therapy for at least six months prior.
Read: The vaccines are an “an effective strategy for preventing COVID-19 in cancer patients,” although that may be muddied when it comes to patients on immunosuppressive therapies. Researchers suggested doing future trials to determine whether patients would benefit from booster shots or post-vaccination serology testing.
Those results were similar to another study shared during ESMO, which found that the Pfizer-BioNTech mRNA jab specifically was nearly as effective and safe in cancer patients when compared with the general population.
The findings were part of a subgroup analysis from Pfizer’s global phase 3 studies, which included patients with cancer history, either ongoing or not. The most common solid cancers were breast, prostate and melanoma among more than 1,600 patients not on active immunosuppressive treatment.
Pfizer’s vaccine was 89.7% effective for patients aged 12 and older, with three COVID-19 cases reported in the vaccine arm and 27 reported among placebo recipients two weeks after their second dose.
That “compares favorably” with Pfizer’s overall vaccine efficacy of 91.1%, researchers determined. While the shot did bring along more side effects than placebo, the most common reports were injection site pain and fatigue.
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Israel, which has already started vaccinating cancer patients with Pfizer’s vaccine since January, has largely served as a barometer for the U.S.’s own vaccination efforts. In a third study presented at ESMO, 232 cancer patients on active treatment in the country were enrolled after being inoculated with Pfizer’s jab.
Researchers then collected serum after each dose and compared it with an age-matched cohort of healthcare workers. They also deployed questionnaires to determine adverse reactions.
Following a first dose, 29% of cancer patients were seropositive compared with 84% in the healthcare group. After a second dose, that shot up to 86%, indicating that the jab appears to be effective in terms of antibody production even though there’s “a pronounced lag” between doses.
The researchers suggested conducting more studies to determine how long the vaccine's protection might last depending on the type of anticancer treatment a patient is using.