“Getting a flu shot can give you the flu.”

It's a widely held belief that receiving a flu shot can actually cause you to contract the influenza virus. This misconception often arises because some individuals experience mild, temporary symptoms after vaccination, such as a low-grade fever, muscle aches, or soreness at the injection site. These reactions are often mistaken for the flu itself, leading people to believe the vaccine made them sick. However, these are simply signs that your immune system is successfully building protection, not evidence of an infection.

Scientifically, the flu shot cannot give you the flu because it does not contain a live, active virus capable of causing illness. The injectable flu vaccine is made with inactivated (killed) flu viruses or only a single protein from the virus, which means it is impossible for them to replicate and cause an infection. Even the nasal spray flu vaccine, which contains live viruses, uses weakened versions that are "cold-adapted," meaning they can only grow in the cooler temperatures of the nasal passages and cannot survive in the warmer environment of the lungs to cause full-blown influenza. The first inactivated flu vaccines were developed in the mid-1940s after the influenza virus was isolated in the 1930s, establishing a long history of safe and effective vaccine technology.

Another reason this myth persists is timing. People might be exposed to the flu virus or another respiratory illness shortly before or during the two-week period it takes for the vaccine to provide full protection. If they become sick during this window, they may wrongly attribute their illness to the recent vaccination. Understanding that the mild side effects are a normal immune response and that the vaccine does not contain infectious virus particles helps to clarify why this common belief is incorrect.