It's a question that has been on the minds of researchers and oncologists long before the Pfizer and Moderna vaccine rollouts began. Although there is a consensus that the vaccines are safe for most cancer patients, according to the American Cancer Society and others in the medical community, research into whether they will be effective for cancer patients is still a data-free zone.

The American Cancer Society recommends that cancer patients talk to their doctors before getting any type of vaccine because all patients and their courses of treatment are different.

There are several factors that may require a cancer patient to delay vaccination, including recent stem cell transplants or other recent use of therapy agents known to reduce vaccine efficacy, according to Dr. Laura Makaroff, the American Cancer Society's Senior Vice President for Prevention and Early Detection.

"As far as safety of the vaccine, every situation for every patient with cancer is a little different. And there's a spectrum of where any one patient might be in their cancer journey," Makaroff told CNN. "The Covid-19 vaccine is definitely safe for people with cancer but it's important that patients have a conversation with their healthcare provider and their cancer care team to determine when is the right time to have the vaccine."

"All the guidance that we're seeing -- the American Cancer society and other leading oncology groups -- is that Covid-19 immunization is recommended for patients in active therapy, but we really understand that there are limited safety and efficacy data on these patients," Makaroff said.

Even with limited data, many cancer experts, medical groups, and doctors are making a big push for vaccinating most cancer patients -- especially those cancer patients most at risk during the pandemic."The potential benefits far outweigh the risks," said Dr. Brian Koffman, chief medical officer for CLL Society, a group that represents patients with chronic lymphocytic leukemia, the most common adult form of leukemia in the western world.

"Despite the lack of safety data specifically in patients with CLL (chronic lymphocytic leukemia), SARS-Cov-2 vaccination is anticipated to be safe."
Patients with chronic lymphocytic leukemia who develop symptomatic Covid-19 have an 89% risk of hospitalization, Koffman told CNN, based on a study published in the journal Nature.CLL is characterized by a weakened immune system. The immunocompromization is so severe that CLL patients are advised to avoid live vaccines such as the ones for measles or yellow fever.

And a weakened immune system also means these cancer patients have an increased risk of death due to Covid-19, according to Dr. Chaitra Ujjani, a physician at Seattle Cancer Care Alliance and oncology professor at the University of Washington School of Medicine. The Nature study, conducted the by European Research Initiative on CLL, found that the mortality rate for CLL patients with symptomatic coronavirus was 31%.

"The thing that people don't quite realize is that the impaired immune system in CLL patients -- due to the disease or some of the treatments for the disease -- can actually impact your response to vaccination," Ujjani told CNN.
"We recommend the Covid-19 vaccines for our patients ... but we're not really sure how effective it's going to be," she added. "Patients with blood cancers are typically excluded from the clinical trials evaluating the efficacy of the vaccine."