What It Is

The influenza vaccine injection (often called the “flu shot”) is a vaccine that protects against influenza (the flu), a contagious respiratory illness caused by influenza viruses. The injection is usually given in the upper arm muscle.

Types

There are several types of flu shots, but the most common are:

• Inactivated Influenza Vaccine (IIV): Contains killed virus and cannot cause flu.

• Recombinant Influenza Vaccine (RIV): Made without using flu virus or eggs—safe for people with severe egg allergies.

• Adjuvanted or High-Dose Flu Shots: Designed for older adults (65+) to create a stronger immune response.

How It Works

The vaccine exposes your immune system to antigens (proteins from the influenza virus). This helps your body develop antibodies so that if you are exposed to the real virus later, your immune system can fight it off more effectively and quickly.

Who Should Get It

• Everyone 6 months and older is recommended to get the flu shot each year (unless they have a specific contraindication).

• High-priority groups include:

  • Adults over 65

  • Pregnant people

  • Young children

  • People with chronic conditions (diabetes, heart disease, lung disease)

  • Healthcare workers

When to Get It

• Ideally before the flu season starts (early fall is best), but it can still be beneficial later in the season.

• Immunity takes about two weeks to develop after the shot.

Benefits

• Reduces the risk of getting the flu

• Lessens severity if you do get sick

• Protects vulnerable populations through herd immunity

• Lowers risk of flu-related hospitalization, especially for children and older adults

Side Effects

Most side effects are mild and short-lived:

• Soreness, redness, or swelling at injection site

• Low-grade fever

• Fatigue or mild muscle aches
  Severe allergic reactions are very rare.