Most health care providers have multiple examples of patients who refuse to take the flu vaccine because they are convinced the vaccine can cause the flu. These patients may have had their own experiences with illness after receiving the flu vaccine, or friends and relatives may have shared horror stories about their own illnesses after receiving the vaccine. Unfortunately, this belief prevents many people from getting the flu vaccine each year.

So can the flu vaccine really cause the flu?

The Centers for Disease Control and Prevention (CDC) is our national public health institute whose main goal is to protect the public health and safety through the control and prevention of disease, injury, and disability. The CDC and multiple experts in the field of infectious disease have clearly stated that the flu vaccine cannot cause the flu. Scientifically, the viruses contained in the flu vaccine are inactivated (killed or significantly weakened), which means they cannot cause infection. It is much safer to get the vaccine than to risk getting the flu in order to develop immunity.

So how do we explain why some people get sick after taking the flu vaccine?

There are multiple reasons someone may become ill shortly after receiving the flu vaccine. For example, some people get other respiratory illness such as “colds” that cause symptoms very similar to the flu. Colds are quite common during flu season and are very contagious. The flu vaccine only protects against the flu. It cannot prevent colds, bronchitis, sinus infections, pneumonia, stomach viruses or other illnesses.

Another reason some people may become ill after taking the flu vaccine is that they may have been exposed to the flu shortly before getting the vaccine. Because the vaccine takes approximately two weeks to become effective in the body and create immunity, it could not protect them from getting the flu. In addition, the flu virus is very contagious and can be spread up to 24 hours before a person shows symptoms of illness. Therefore many people are exposed to the flu without even knowing it.

Some people experience a reaction to the flu vaccine such as soreness, redness or swelling at the injection site, low-grade fever, headache or mild body aches. These reactions are not the flu but simply the body’s response in order to develop immunity. These symptoms are much less severe than the symptoms caused by actual flu illness. However, they can be mistaken for the flu.

Despite receiving the vaccine, there will be some people who get the flu because they have a weakened immune system that doesn’t allow the vaccine to provide full protection against the flu. This is more likely to occur among people over 65 or those with chronic health conditions. There is now a high-dose flu vaccine approved for people age 65 and over that helps boost their immune response to the flu. Anyone over the age of 65 should discuss this high-dose vaccine with their health care provider.

Flu viruses are constantly changing requiring new flu vaccines be developed each year to protect against the viruses expected to be most prevalent. In February each year, the World Health Organization (WHO) organizes a consultation with multiple agencies from over 100 countries who monitor flu year-round. Based on scientific data from thousands of flu virus samples from patients around the world, WHO makes recommendations for the specific viruses to be included in that year’s flu vaccine. Each country then makes their own decisions about viruses to be included in their country’s vaccine. In the U.S., the Food and Drug Administration (FDA) makes the final decision about viruses to be included in the current year’s flu vaccine. Once this decision is made, the vaccines must then be manufactured and sent out to health care providers, clinics and pharmacies before the flu season begins.

The ability of the vaccine to protect a person depends largely on the “match” between viruses selected to make the vaccine and those spreading and causing illness. Some years the match is very good and the vaccine is very protective. But because flu viruses are constantly changing, the vaccine composition is not always a good match. There is no way to know in any given year if the vaccine match is good until the flu season starts and patient samples are tested to determine which viruses are spreading.

So despite vaccination, some people may get exposed to a flu virus that is very different from the viruses that the vaccine is designed to protect against. However, even during years when the virus match is not excellent, the flu vaccine (which contains 4 different flu viruses) can still protect against one or more of the viruses causing illness that year.

So the answer to the age-old question “Can I get the flu from the flu vaccine?” is clearly “NO”! You may still get sick, but it won’t be because of the flu vaccine.

Flu vaccines are currently available in most medical offices, pharmacies, health departments and walk-in clinics. The sooner you get the flu vaccine, the sooner you are protected against the flu. If you are unsure about getting a flu vaccine, always consult with your health care provider.

Debbie Edelen, APRN is an advanced practice provider at North Garrard Family Medical Center, a service of Ephraim McDowell Health.