COVID-19 is twice as likely to be fatal for patients who also have cancer than patients without cancer.

That’s why the American Association for Cancer Research last month recommended that cancer patients be considered for priority access to the two new COVID-19 vaccines.

An AACR task force reviewed the medical literature and found that even when age, sex, and chronic illnesses were taken into account, cancer patients had a greater risk for severe COVID-19 disease and death.

Still, cancer patients may be hesitant. Nearly all vaccine clinical trials — including trials of the Pfizer-BioNTech and Moderna shots that are now authorized for emergency use — excluded people being treated for cancer because their immune systems may be compromised. Cancer patients will be included in ongoing trials, but for now, safety and effectiveness data for this group are not available.

Because COVID-19 vaccine supplies are limited, it may be months before cancer patients have the opportunity to roll up their sleeves. Meanwhile, cancer organizations urge patients and their oncologists to discuss the issue.

We asked Tracey L. Evans, director of thoracic oncology research at Lankenau Institute for Medical Research and co-director of the thoracic oncology program at Main Line Health, to talk about the risks and benefits of vaccination for cancer patients, as well as for those who have finished treatment.

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There are numerous types of cancer treatment, including chemotherapy, radiation, hormone therapy, stem-cell transplants, and newer immunotherapies. Are they all harmful to immune function, and which are most harmful?

Traditional chemotherapy indiscriminately attacks faster growing cells, and often wipes out white blood cells, a vital part of the immune system, in addition to damaging the delicate linings of the gastrointestinal tract. Chemotherapy usually has the biggest impact on the immune system.

Patients undergoing stem-cell, or bone marrow, transplant experience temporary eradication of their bone marrow, including their white blood cells, so these patients are the most immune suppressed and the most at risk for dangerous infections.

Radiation is targeted to specific tissues with cancer, so adjacent normal structures may be caught in the line of fire. Radiation to the pelvis, for example, can temporarily halt the function of the bone marrow and lead to general immune suppression.

Hormonal therapies, used to treat prostate and breast cancer, usually have minimal impact on the immune system. Newer immunotherapies such as checkpoint inhibitors actually activate some parts of the immune system to kill cancer cells, but they can also trigger autoimmune side effects as well as potentially dangerous immune responses to infections.

Both new vaccines are novel in that they use a bit of genetic code, called messenger RNA, to prime the immune system to recognize and ward off the coronavirus. Neither vaccine caused serious side effects in trials, but many patients experienced temporary flu-like symptoms, including fatigue, headache, and chills. What are some concerns about giving the vaccine to cancer patients?

Paradoxically, many of the symptoms we experience during an infection are not from the germ itself but rather from our immune system’s response. Examples of such responses include fever and increased mucus production, as well as headache, fatigue, and chills. So it makes sense that after getting a COVID-19 vaccine that awakened the immune system, recipients felt the effects; that meant the vaccine was doing its job. The side effects of the COVID-19 vaccines are typically short-lived and predictable, but the potential complications of the disease are unpredictable and can be deadly. My first patient diagnosed with COVID was a woman who had metastatic lung cancer. She had been doing very well for two years on immunotherapy. She was unknowingly exposed to the virus by a family member, and she was dead just a week later. I wish this vaccine had been available to her.

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The vaccines are reportedly about 95% effective at preventing coronavirus infection. Do you think that benefit would outweigh any risks for cancer patients?

Because the m-RNA vaccines do not include any virus, there is no risk of contracting the infection from getting the vaccine. Therefore, the risks from the vaccine should be negligible regardless of who receives it. There have been several reports of a severe allergic reaction known as anaphylaxis — a dangerous overreaction of the immune system. Fortunately, this has been very rare and can be treated with epinephrine.

Because some cancer patients are already weak and debilitated, there is a small chance that vaccine side effects could make them slightly more weak and debilitated, increasing their risks of other serious infections such as pneumonia. Oncologists must think about this issue when prescribing a new anticancer treatment: Will the side effects of the treatment be worse than the disease? I think a potentially greater concern, given that many cancer patients have impaired immune systems, is whether the vaccines will work as well for them as for those in the clinical trials. Still, some protection would be better than none. I would just caution cancer patients getting the vaccine that immunity to the coronavirus may not be guaranteed, and we do need data on effectiveness.

The seasonal flu shot is recommended for cancer patients because the flu is so dangerous for them. The flu vaccine primes the immune system using an inactivated flu virus or a single protein from the microbe. Does flu vaccination offer any insights for COVID-19 vaccination?

Absolutely. Like COVID-19, seasonal flu is much more dangerous in patients who are older, frail, or have serious illnesses such as cancer. The flu vaccine is only moderately protective, and in cancer patients, the protection is even less. Still, studies clearly show that flu shots reduce the likelihood and severity of the flu for everyone, including cancer patients. We also emphasize that cancer patients’ close contacts should get the flu shot to provide additional layers of protection. One of the main reasons health providers are first in line to get the COVID-19 vaccine is to make sure we don’t expose our patients to this disease.

After cancer treatment ends, does the immune system recover and how is this evaluated? Should people in remission or long-term survivors with normal immune function be urged to get the vaccine?

The most objective measure of immune function in cancer patients on chemotherapy is the neutrophil count. Neutrophils, which are a subtype of white blood cells, are the primary defense against bacterial infections. They usually drop to a low point 10 to 14 days after chemotherapy and then recover. By four weeks after a chemo cycle, most patients have full recovery of their neutrophil count. The performance of other parts of the immune system, such as T cells, is harder to measure, but may be disrupted long after cancer treatments are completed. Therefore, even patients in remission and long-term survivors may have impaired immune responses. That’s why I would urge anyone with a history of cancer to get vaccinated against COVID-19.