Flu Shot Myths Persist Despite Scientific Consensus, Experts Say

Nearly 30 percent of Americans believe that getting a flu shot can cause influenza, according to recent surveys, despite clear scientific evidence to the contrary. Health experts are working to dispel this persistent misconception as flu season approaches.

“No flu vaccine can cause the flu,” said Dr. Samantha Picking, senior director of immunizations at Walgreens, in an interview. “Most flu vaccines do not contain a live virus and use an inactive flu virus or pieces of the virus.”

This widespread belief likely stems from the vaccine’s common side effects, which can include headache, fever, nausea, muscle aches, and localized reactions at the injection site like soreness and redness. These symptoms, while similar to mild flu symptoms, are actually signs that the body’s immune system is responding appropriately to the vaccine.

Dr. Marc Siegel, Fox News senior medical analyst, reinforced this point, explaining that the standard flu shot is formulated from a “dead, inactivated or killed virus,” making it impossible to contract influenza from the vaccination itself.

The nasal spray version of the flu vaccine does contain a live-attenuated influenza virus (LAIV), but this is an extremely weakened form of the virus that cannot cause a full-blown infection in healthy individuals.

When side effects do occur, they typically begin shortly after vaccination and last only one to two days. “If you do experience common side effects like aches, low-grade fever, or pain and swelling at the injection site, it means the vaccine is working,” Dr. Picking noted.

Some demographics are more likely to experience side effects, including women, children under five, pregnant women, and older adults receiving high-dose vaccines. Most reactions remain mild and can be managed with over-the-counter medications as recommended by pharmacists.

While it is possible to get the flu soon after vaccination, this isn’t because the shot caused the illness. “It takes around two weeks for your body to develop full immunity after getting vaccinated, so you can still contract the flu shortly after receiving your flu shot,” Dr. Picking explained. “If that happens, the illness didn’t come from the vaccine — it’s simply because your body wasn’t fully protected yet.”

This timing factor highlights the importance of early vaccination before the peak of flu season, which typically runs from October through May in the United States, with activity often peaking between December and February.

For those concerned about distinguishing between vaccine side effects and actual flu symptoms, experts point to key differences: vaccine reactions tend to be milder, appear within hours of the shot, and typically resolve within a few days. In contrast, actual influenza symptoms are generally more severe and prolonged, often lasting a week or more and potentially accompanied by complications in vulnerable populations.

Public health officials continue to recommend annual flu vaccination for everyone six months and older, with few exceptions. The U.S. Centers for Disease Control and Prevention estimates that flu vaccination prevents millions of illnesses and tens of thousands of hospitalizations each year.

For those wondering about timing their vaccination while already feeling under the weather, Dr. Picking advises that it’s generally safe to get the flu shot with a mild illness, such as a cold without fever. However, those experiencing moderate or severe illness, especially with fever, should wait until recovery before getting vaccinated to ensure an optimal immune response and to avoid confusing illness symptoms with vaccine side effects.

As flu activity increases nationwide, with some states like New York already reporting record-breaking numbers this season, health experts emphasize that vaccination remains the most effective prevention tool available, despite persistent misconceptions about its safety and efficacy.