Researchers have found lower immune response to the COVID-19 vaccine in cancer patients on active chemotherapy.
A third dose of the Pfizer vaccine boosted immune response.
The COVID-19 pandemic has been an especially stressful time for cancer patients undergoing chemotherapy, which attacks not only the cancer, but also the immune cells needed to defend the body from infections.
“We wanted to make sure we understand the level of protection the COVID-19 vaccines are offering our cancer patients, especially as restrictions were being eased and more contagious variants were starting to spread,” says Rachna Shroff, chief of gastrointestinal medical oncology at the University of Arizona Cancer Center and director of the Cancer Center Clinical Trials Office.
To answer this question, Shroff and a team of researchers looked at 53 Cancer Center patients on immunosuppressive active cancer therapy, such as chemotherapy. They compared the immune response following the first and second dose of the Pfizer COVID-19 vaccine with that of 50 healthy adults.
After two vaccine doses, most of the cancer patients showed some immune response to the vaccine, meaning they had antibodies for SARS-CoV-2, the virus that causes COVID-19.
“We were pleasantly surprised,” says Deepta Bhattacharya, professor of immunobiology in the College of Medicine-Tucson and a member of the Cancer Center and BIO5 Institute. “We looked at antibodies, B cells, and T cells, which make up the body’s defense system, and found the vaccine is likely to be at least partially protective for most people on chemotherapy.”
However, the immune response was much lower than in healthy adults, and a few of the patients had no response to the COVID-19 vaccine. This translates to less protection against SARS-CoV-2, especially the delta variant that is now the dominant strain in the United States.
Twenty patients returned for a third shot, which boosted the immune response for most. The overall group immune response after the third shot reached levels similar to those of people who were not on chemotherapy after two doses.
The interdisciplinary research team was formed not long after the Pfizer vaccine was approved in late 2020. To get the clearest answer possible, they focused on patients with solid tumors, such as breast or gastrointestinal cancer, and excluded people on immunotherapy.
The results appear in the journal Nature Medicine.
Source: University of Arizona
