In a fourth study, Thakkar et al assessed responses to vaccination with the Pfizer-BioNTech, Moderna, or Johnson & Johnson vaccine. Seroconversion rates were 98% among the 134 patients with solid tumors and 85% among the 66 patients with hematologic malignancies (P =.001).5 

The rate of seroconversion was significantly lower in patients on active chemotherapy than in all other cancer patients (92% vs 99%; P =.04). Rates of seroconversion were high in patients who received hormone therapy (100%) or immune checkpoint inhibitors (97%) but lower in patients who received a stem cell transplant (73%), anti-CD20 therapies (70%), or chimeric antigen receptor T-cell therapy (0%). 

In a preprint article that has yet to be peer reviewed, Shroff et al reported immune responses to the Pfizer-BioNTech vaccine, comparing 50 healthy control individuals and 53 patients with solid tumors who were receiving chemotherapy.6 


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The researchers found that 67% of the cancer patients developed neutralizing antibodies after the first immunization, and that number went up to 80% after the second immunization. In comparison, 98% and 100% of the healthy control individuals had detectable neutralizing antibodies after the first and second immunizations, respectively. 

“When you look at the totality of the data, I think it is fair to say that patients who are immunocompromised, whether that be active cancer therapy, hematologic malignancy, solid tumor, and then frankly even organ transplant, do not have the same immunity,” said lead author of the preprint Rachna Shroff, MD, medical director of the University of Arizona Cancer Center Clinical Trials Office in Tucson.6 

Dr Shroff added that these data probably contributed to the US Food and Drug Administration’s recent decision to authorize an additional dose of COVID-19 vaccines for immunocompromised people.7 

Certain cancer patients fall into this category.8 This includes patients with solid tumors receiving chemotherapy — and, in some cases, immunotherapy — currently or within the last 6 months. It also includes patients receiving treatment for hematologic malignancies now or within the last 6 months. 

Boosting Immunity

Researchers are currently investigating the efficacy of a third vaccine dose for cancer patients in a study at Montefiore Medical Center in New York City. The researchers are screening cancer patients at Montefiore to identify those who do not have detectable antibodies 2 weeks after immunization with the Pfizer-BioNTech, Moderna, or Johnson & Johnson vaccine. 

The researchers are giving those patients an additional dose of the Pfizer-BioNTech vaccine and checking their antibodies 4 weeks after the additional dose. 

The study will probably enroll more patients with hematologic malignancies than solid tumors because solid tumor patients are more likely to develop antibodies following immunization, noted Astha Thakkar, MD, a hematology-oncology fellow at Montefiore Medical Center who is involved in the booster study and is the lead author of one of the aforementioned published studies.5

The goal of the booster study is not only to help the subset of cancer patients who fail to mount an immune response after vaccination. Researchers are also theorizing that the booster dose may improve the duration of vaccine protection.