SearchYou’ve probably heard about the flu shot before—maybe more times than you can count. And if you’ve already made up your mind, it can be easy to tune out yet another article on the topic. This isn’t about pressure or persuasion. It’s simply a look at how the flu shot works and why some people include it as part of their seasonal health routine.
Each year, flu vaccines are updated using information from year-round monitoring of flu cases around the world, collected through hospitals, clinics, and public health laboratories that track which strains are circulating. Laboratories analyze patient samples to identify which flu strains are circulating most widely and scientists review this global data to help determine which strains are included in the seasonal flu vaccine. This ongoing process is why the flu shot is updated from year to year.
While no vaccine is 100% effective, studies show that seasonal flu vaccination can reduce the risk of severe illness and complications—especially for older adults, young children and people with certain health conditions.
Common Symptoms of the Flu
Flu symptoms often come on more suddenly than a common cold. Symptoms can range from mild to severe and may last several days or longer, depending on the person. Flu symptoms may include:
- Fever or feeling feverish
- Chills
- Fatigue or extreme tiredness
- Muscle or body aches
- Headache
- Cough
- Sore throat
- Runny or stuffy nose
- Nausea, vomiting, or diarrhea (more common in children)
How the Vaccine Works
At a basic level, the flu shot works by helping the immune system recognize flu viruses before someone is exposed. The vaccine contains inactive pieces of the virus that cannot cause the flu but do allow the immune system to practice recognizing it. When this happens, the immune system begins building antibodies that help it recognize and respond to the flu more quickly if exposure happens later. Because the immune system has already been introduced to the virus, it can respond faster and more efficiently.
Vaccine Benefits
Research shows that this type of immune preparation is often associated with milder illness and fewer complications if someone does get sick. Some people experience mild side effects after a flu shot, such as a sore arm or brief fatigue. These reactions are signs that the immune system is responding and learning—not that someone has the flu. For many people, getting a flu shot is one way to support overall health during flu season, alongside rest, nutrition and regular preventive care.