Why Get a Flu Shot?

By: Dr. Kai-Ming Chang, Division of Infectious Diseases

Every fall and winter, patients and family members often ask me questions like: “My health isn’t great. Can I still get a flu shot?” or “I heard you can still get sick after the shot, so what’s the point?” Behind these questions is a common misunderstanding about influenza and what vaccination actually does.

The flu shot is not something only cancer patients or people with weak immune systems need. It is basic protection recommended for everyone age 6 months and older. Influenza spreads easily and changes quickly. Regardless of age or health status, anyone can get infected. Many people assume, “I’m young and healthy, so I don’t need to worry about the flu,” but every year there are cases of people who end up in the ICU or even die from influenza, including some who are relatively young and do not have chronic illnesses.

It is also important to be clear about what the vaccine can and cannot do. The flu shot does not make you “immune to everything.” It does not guarantee you will not get respiratory infections, and it does not promise you will never get the flu. What it does very well is lower the risk of severe illness, complications, and death from influenza. 

If Your Health Is Poor, You Need Protection Even More

Some people think, “If my body is weak, I shouldn’t get vaccines.” In reality, it is usually the opposite. People with weaker immune function have a higher chance of becoming seriously ill if they catch the flu. This is especially true for cancer patients receiving chemotherapy. If influenza strikes in the middle of treatment, it can delay therapy and can be life-threatening.

That is why I often remind patients and caregivers: it is not “my health is poor, so I can’t get vaccinated.” It is “my health is poor, so I should be protected.” Even if a person’s immune response to vaccination is not as strong as someone who is fully healthy, some protection is still far better than none. 

Flu Vaccine Safety: What Side Effects to Expect

Some patients worry, “If my immune system is weak, will I have more side effects?” A weaker immune system does not automatically mean a higher risk of side effects.

Influenza vaccines have been used for decades and are widely considered safe. Before any flu vaccine is approved for use, it must demonstrate both effectiveness and safety through multiple phases of clinical testing. Most side effects, when they occur, are mild and short-lived.

The most common reactions are local symptoms at the injection site, such as soreness, redness, swelling, or itching. Some people may have mild whole-body symptoms such as low-grade fever, headache, or muscle aches, which usually improve on their own within one to two days. Serious reactions, such as immediate severe allergy symptoms (trouble breathing, hoarseness, rapid heartbeat, confusion) are very rare. Rare neurologic conditions that people often fear, such as Guillain-Barré syndrome, are also uncommon. 

From a clinician’s perspective, what is more concerning than “something might happen after the vaccine” is “someone who should have been vaccinated ends up catching influenza and deteriorates.”

Timing and Who Should Get Vaccinated

For cancer patients actively receiving treatment (such as chemotherapy), the issue is usually not whether you can get a flu shot, but when to get it. The best approach is to discuss timing with your primary cancer physician so you can choose the safest and most appropriate point during the treatment cycle. 

Some special situations require more structured planning. For example, after a bone marrow or hematopoietic stem cell transplant, immune function can remain low for one to two years. In those cases, transplant teams often coordinate with infectious disease specialists to map out a full vaccination schedule. In general, many patients can begin influenza vaccination around three months after transplant, then add other vaccines based on their individual situation and recovery.

Vaccination is not only about the patient. Family members and primary caregivers should also be vaccinated. When people close to the patient are protected, it creates a “protective buffer” that reduces the patient’s exposure risk.

As for brand choice, it usually does not need to be complicated. Some patients delay vaccination while waiting for a specific product and end up missing the best window. In practice, any appropriately approved flu vaccine can provide meaningful protection against severe outcomes. Getting vaccinated on time matters more than waiting.

Beyond Flu: Other Vaccines Worth Discussing

Depending on your age, health conditions, and treatment plan, it can also be wise to discuss other vaccines with your care team, in addition to COVID-19 boosters. For young children and older adults, and for some patients receiving immunosuppressive medications or radiation therapy for malignancy, pneumococcal vaccination can help prevent serious infections such as pneumonia, bloodstream infection, and meningitis. 

Shingles vaccination is also important for many people. In the U.S., CDC guidance notes that recombinant zoster vaccine (Shingrix) is recommended for adults 19 and older who are or will be immunocompromised, and routinely for adults 50 and older. 

For older adults and people with chronic conditions (such as hypertension, diabetes, cardiovascular disease, cancer) or those receiving immunosuppressive therapy, RSV vaccination may also be worth considering as a way to reduce the risk of RSV-related lower respiratory tract disease.

If you are considering any of these vaccines, discuss with your treating physician whether they can be given at the same visit as the flu shot or whether spacing is better for your specific situation.

A Final Reminder From the Clinic

One of the most painful experiences for an infectious disease physician is seeing a patient who was eligible for vaccination choose not to get it because of hesitation or misunderstanding, and then suffer severe influenza complications. For most people, the protective benefit of vaccination is far greater than the risk of side effects. Do not wait until you are sick to wish you had prevented it. Prevention is almost always more effective than treatment.

Q&A

Q: I’m allergic to eggs. Can I still get a flu shot?

A: Yes. Current CDC guidance states that people with egg allergy can receive any flu vaccine (egg-based or non-egg-based) that is appropriate for their age and health status, and egg allergy does not require extra safety measures beyond standard vaccination practices. 

If you still feel uneasy, you can ask about cell-culture-based influenza vaccines (for example, Flucelvax Quad). Unless you have had a severe allergic reaction to a previous influenza vaccine or another vaccine component, you generally do not need special extended observation after vaccination. 

Q: How do I schedule a flu shot?

A: You can ask during your regular clinic visit with your primary physician. You may also use KFSYSCC’s vaccine appointment platform to book a vaccination.