Flu is a contagious disease caused by the influenza virus. The viral disease spreads around the United States each year, usually from October through May. The flu is spread mainly through close contact, coughing, and sneezing.

Flu symptoms may include:

– fever/chills
– sore throat
– muscle aches
– fatigue
– cough
– headache
– runny or stuffy nose

Anyone can get the flu, but it is more dangerous for some individuals. Infants, young children, pregnant mothers, individuals 65 years old or older, and people with certain health conditions or a weakened immune system are at the highest risk. Flu can lead to blood infections and pneumonia. It can also cause seizures and diarrhea in children. Each year thousands of individuals die from the flu within the United States and many more are hospitalized.

The Flu Shot

The best way to prevent the flu is by getting a flu vaccination each year. Flu vaccines cause antibodies to develop in the body and the antibodies provide protection against the influenza viruses.

Flu vaccine can:

– Prevent individuals from getting the flu
– Make the flu less severe
– Keep individuals from spreading the flu to family, friends, and other people in the community

Flu shots do not contain a live virus and they cannot cause the flu. The seasonal flu vaccine protects against influenza viruses. Each year research is conducted to determine the vaccine makeup that will provide protection against influenza viruses for the upcoming flu season. It takes about two weeks for protection to develop after a flu vaccination and protection lasts through the flu season. Even if the vaccine doesn’t exactly match the viruses in circulation it still provides some protection.

It is important to get vaccinated every year for two important reasons.

1. The body’s immune response system developed from a vaccination declines over time and annual flu vaccinations helps create optimal protection.
2. The vaccine composition is updated annually, based on research showing the best protection against flu viruses for the upcoming season as well as effectiveness of the previous season’s vaccine.

For the best protection, everyone 6 months and older, who is an approved candidate, should get vaccinated annually.

Vaccine formulation

For the past ten flu seasons the U.S. has primarily distributed a quadrivalent flu vaccine, with four influenza virus strains included in the vaccine. For the 2024-2025 flu season all flu vaccines distributed in the U.S. will be trivalent, meaning only three influenza viruses will be included in the vaccine.

The trivalent formulation is eliminating the B/Yamagata viruses. The influenza B/Yamagata vaccine component is being removed because influenza B/Yamagata viruses have not been detected since March of 2020, based on global surveillance.

Since the B/Yamagata viruses are not actively circulating in people, the risk of infection with the B/Yamagata lineage viruses is very low. The B/Yamagata viruses essentially no longer pose a threat, so individuals for the current season do not need to be vaccinated against them.  

Resources:

Influenza Vaccine Information Statement

www.cdc.gov/flu