Six months after receiving the second dose of the Pfizer vaccine, the level of antibodies in cancer patients with solid tumors is reduced, but similar to that observed in the general population. The vaccine also appears to be safe and without any particular adverse effects for such patients, two studies by researchers at Rambam Medical Center in Haifa have shown.
A study led by Prof. Irit Ben-Aharon, director of the Oncology Center at Rambam Hospital, whose findings were published in Cancer Discovery, a journal of the American Association for Cancer Research, monitored 154 patients actively undergoing treatment for about half a year after the second dose of the Pfizer vaccine, and compared the results with those of 135 healthy controls.
“Since the beginning of the pandemic, we have been following a group of cancer patients on active treatment for solid tumors, to see all the clinical outcomes of the disease. And when vaccination began, we looked into both the safety and efficacy of the inoculation,” Aharon said. “We used healthcare workers for the control group.
“The age was a key issue as the antibody response was correlated with the age of the individuals,” she added.
In the first part of the study, published a few months ago, researchers reported that only 30% of the patients developed antibodies after the first shot, but after the second, the response was similar to the one of the general population: 79% compared to 84%.
They continued to follow the patients for the following six months.
“We were surprised to see that the level in cancer patients decreased in a similar way to that of the general population, not worse,” Aharon noted. “This was not what we expected because some of these patients are going through treatment that affects the immune system.”
Among those who did not develop antibodies, most – some 81% – were chemotherapy patients, “which makes sense because chemotherapy is a treatment that is known to hamper immune response,” Aharon noted.
While no specific difference was detected between different types of solid tumors, for other types of cancer, such as blood cancers, other studies showed that the response to the vaccine was much lower, she remarked.
Aharon said that in terms of getting a booster, solid tumor patients are recommended to get it.
In addition, another study, whose findings were recently published in the Journal of the American Medical Association, focused on assessing vaccine safety for cancer patients.
It considered 232 patients in active treatment and 261 healthcare workers as controls. It found a similar antibody response after the second dose – 86% developed antibodies – and no specific adverse effects.