comscoreFlu Shot: Q&A

What is a flu shot?

The flu shot, or seasonal influenza vaccine, is a mixture of dead flu viruses that prepares the immune system to fight the actual viruses if they enter the body. The immune system remembers the viruses in the flu shot and is ready to launch a response if they show up in your body. After you get the shot, it takes about 2 weeks for your body to develop antibodies that can help protect you against infection from the viruses.

It’s important to get a flu shot every year. The influenza viruses used in the flu shot vary from year to year, depending on researchers’ predictions about which ones are likely to be going around that year. You’ll want to make sure you’re protected.

Getting the shot doesn’t guarantee you won't get the flu, but it does mean that you have a much smaller chance of getting sick from it.


Why is the flu shot important for people affected by breast cancer?

Getting a flu shot is particularly important for people with weak immune systems because they are the ones who are the most vulnerable to serious complications if they actually catch the flu. These people include babies, the elderly, people with allergies, and people with chronic or acute illnesses. Since breast cancer treatments can weaken your immune system, it is especially important for you to get a flu shot. According to the Centers for Disease Control and Prevention (CDC), people who have cancer or had it in the past are at higher risk of flu complications. The CDC also recommends that anyone who lives with you should receive the regular flu vaccine as well (but not Flu-mist, which is made from a live virus).

Aging also weakens the immune system, increasing the risk of complications from flu. If you are age 65 or older, ask your doctor about the new high-dose flu vaccines that are available for people over 65.


When should you get the flu shot?

The CDC recommends getting the seasonal flu shot as soon as it becomes available in your community — typically in the early fall. Although we tend to associate flu with the winter months, flu season can begin as early as October.

People receiving chemotherapy can get the flu shot at any time. However, your doctor might advise you to wait and get the shot when your white blood cell count is at a peak, usually a day or so before your next cycle of chemotherapy is about to begin. There are two reasons for this:

  • The higher your white blood cell count, the more effective the shot is likely to be. Remember that the flu shot is going to “teach” these cells and your entire immune system how to deal with the influenza viruses should they enter your body. The more white blood cells that are present to respond to the viruses in the vaccine, the better.

  • Any side effects of the flu shot might be confused with infection. Although most people don’t have side effects, some can experience soreness, swelling, fever, and/or body aches. Your doctor will be watching you closely for any symptoms of infection, especially when your white blood cell counts are lowest.

If your white blood cell counts are staying low throughout your chemotherapy and you need a flu shot, you should still get one. If you’re experiencing any serious side effects from chemotherapy, such as fever or chills or possible symptoms of infection, your doctor may want to delay the flu shot until these improve.

Bottom line: Talk to your doctor about the best timing for your flu shot. Ideally, it’s before chemotherapy begins. If you’re working with your primary care physician, be sure to get the OK from your cancer doctors, too.


Does the flu shot have side effects?

In some people, the flu shot may cause mild side effects including soreness, redness, or swelling where the shot was given; fever; and aches. These mild symptoms usually begin soon after the shot is given and can last 1 to 2 days.

Like any medication, the flu shot can cause a serious allergic reaction, but this risk is very small. If you have any unusual problems a few minutes to a few hours after getting the shot, such as high fever, difficulty breathing, hives, weakness, or dizziness, call your doctor right away.

The virus in the flu shot is developed in egg products. If you are allergic to eggs, discuss with your doctor whether you should get the shot.


Who should give you the flu shot?

Any qualified medical person can administer the flu shot — a nurse, a pharmacist, or your doctor. However, some insurance plans cover the flu shot only if you get it from your primary physician. Find out what your policy covers before you decide where to get the shot.

— Last updated on June 29, 2022, 3:11 PM