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Influenza in Oncologic Setting
Overcoming Barriers to Influenza Treatment in the Oncologic Setting

Released: November 22, 2022

Expiration: November 21, 2023

Derrick W. Su
Derrick W. Su, MD
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Key Takeaways

  • Patients with cancer have a significantly increased risk of morbidity and mortality with influenza.
  • During flu season, patients should be counseled on recognizing the difference between cancer- or treatment-related symptoms and flu symptoms.
  • Preventative measures with vaccination, appropriate patient counseling, and improving healthcare professionals’ comfort levels with recognizing and treating influenza all help to protect patients with cancer.

Adults undergoing active cancer treatments are one of the most vulnerable populations when it comes to infections, and influenza is no exception. While concern over the seasonal flu was overshadowed by that of COVID-19 pandemic, it is important to remember that patients with cancer still have a significantly increased risk of morbidity and mortality from flu.

Prevention With Vaccination
Much like many cancers in general, prevention is the key to reducing the risk of serious illness with influenza. The American Society of Clinical Oncology (ASCO) and the Infectious Disease Society of America (IDSA) recommend that all patients undergoing chemotherapy should receive an inactivated flu shot every year. However, effectively vaccinating against the flu in these patients can be complicated, particularly as it relates to the timing of the shot. Ideally, for the vaccine to be effective, it should be administered when the immune system is intact and able to mount a sufficient immunogenic response. How to actually do this in practice is unclear. One recommendation is to give the vaccine in between chemotherapy cycles ( ie, at least 1 week after the last treatment, or at least 2 weeks before treatment starts). However, patients undergoing treatment with anti-CD20 monoclonal antibodies in hematologic malignancies mount an even lower immune response since the drug preferentially knocks out the very part of the immune system that produces infection fighting antibodies.

So, what do we do in this situation? In my view, having some protection, even very little, is better than none at all. If possible, patients should be offered the opportunity to update their vaccines prior to starting cancer treatment. If treatment is time critical, then once the disease is stabilized, arrangements should be made for the patient to receive vaccinations in between cycles of chemotherapy. For all providers who take care of patients with cancer, asking and counseling about the flu vaccine should be integrated into each routine health maintenance visit. Aside from vaccination, some of the measures now widely adopted for protecting from infection with COVID-19—such as social distancing, mask wearing, and proper hand hygiene—can protect from infection with the flu as well, and patients undergoing chemotherapy should be counseled to implement these strategies particularly in high-risk situations.

Recognizing Symptom
If a patient undergoing cancer treatment contracts the flu, appropriate diagnosis and timely treatment can mean the difference between life and death. To be fair, influenza cases dropped to historic lows during the COVID-19 pandemic, however, mortality rates with influenza were not insignificant. In an observational cohort study in Germany, Kodde and colleagues looked at patients admitted with either COVID-19 or influenza between 2016 and 2021 and found that about 35% of cancer patients died from COVID-19, whereas 18% died from flu.

Patients with cancer contend with a weakened immune system either from the disease itself, or neutropenia and impaired T-cell function from treatment. Abdel-Rahman and colleagues found that certain subtypes of diseases, such as lung cancer, head and neck cancer, and hematologic malignancies, are also associated with a higher risk of death from influenza and pneumonia. Even when feeling ill, patients may not necessarily recognize that their symptoms are due to the flu. Side effects from the myriad cancer treatments we have today can range broadly, and some can even mimic flu symptoms, such as fatigue, muscle aches, headaches, and GI symptoms like nausea, vomiting, and diarrhea. Furthermore, while patients at risk for neutropenic fever are typically taught to recognize a temperature of 100.4° F as the trigger to call their oncologist, a true fever may not necessarily be present in influenza infections. During flu season, patients should be counseled on recognizing the difference between cancer- or treatment-related symptoms and flu symptoms.

Testing and Evaluation for Treatment
There are easily available antivirals for influenza. However, even if patients present appropriately to their oncologists with concern for the flu, testing and clinical evaluation may be impaired. Many facilities still implement blanket rules advising patients not to present to the doctor’s office in person if COVID-19 symptoms are present. Many of these symptoms overlap with those of the flu and requiring the patient to first test negative for COVID-19 before booking an in-person visit may delay the assessment and subsequent treatment initiation for influenza. Also, while COVID-19 home test kits and walk-in PCR testing centers are now ubiquitous, access to influenza testing is not as easy. With COVID-19 infection being the major concern in many patients undergoing cancer treatment, testing negative for COVID-19 on a home test may provide a false sense of security when in fact symptoms may be related to the flu. Unfortunately, during the pandemic, many patients avoid the hospital or healthcare settings even when feeling ill due to fear of being exposed to COVID-19, but instead risk deterioration from the underlying condition. With the concern for a resurgence of influenza this season, I anticipate many patients suffering consequences from delaying diagnosis and treatment of the flu.

Final Thoughts
In 2022, many patients with cancer are living longer and experiencing fewer treatment-related toxicities due to the advancement of targeted therapy, immuno-oncology, and precision medicine. While these novel therapeutics may seem nearly unrecognizable from the chemotherapy available even just 5-10 years ago, many of the negative effects on the immune system persist, and influenza continues to be a serious epidemiologic concern in these patients. Preventative measures with vaccination, appropriate patient counseling, and improving clinician comfort levels with recognizing and treating influenza are important steps to help protect this uniquely vulnerable population.

Your Thoughts?
How do you manage flu in your oncology practice? Join the discussion by posting a comment.