Understanding the flu vaccine

Influenza (flu) is a serious disease that can lead to hospitalization and even death. Every flu season is different, and influenza infection can affect people differently. Millions of people get the flu and can be hospitalized or die from flu-related causes every year.

An annual seasonal flu vaccine is the best way to reduce your risk of getting sick with seasonal flu and spreading it to others. Plus, when more people get vaccinated against the flu, less flu can spread through the community.

Flu vaccines cause antibodies to develop in the body two weeks after vaccination. These antibodies protect against infection with the viruses that are in the vaccine. The seasonal flu vaccine defends you from the influenza viruses that are likely to be most common during the upcoming flu season.

Everyone six months of age and older should get a flu vaccine every flu season. Vaccination to prevent influenza is particularly important for people who are at high risk of serious complications from influenza.

If your child is between 6 months to 8 years old and never had a flu shot or only received one dose before July 1, they will need two doses of the flu vaccine. The two doses must be given at least four weeks apart. Learn more about childhood immunizations.

Talk to your primary care physician if you have concerns about getting a flu shot. Generally, those who meet any of the below criteria should not get the flu vaccine:

• Children less than six months of age
• People who are experiencing a moderate to severe illness with a fever at the time of vaccination
• People with life-threatening allergies to any ingredient in the flu vaccine (such as gelatin)*
• People who previously developed the rare neurological disorder Guillain-Barré syndrome after receiving the seasonal flu vaccine

*People diagnosed with an egg allergy can request an egg-free vaccination

You should get a flu vaccine before flu begins spreading in your community. It takes about two weeks after vaccination for antibodies to develop in the body that protect against flu. Make plans to get vaccinated early in fall before flu season begins.

You should get a flu vaccine in the fall, if possible. Getting vaccinated later can still be beneficial and vaccination should continue to be offered throughout the flu season, even into January or later.

Children who need two doses of vaccine should start the vaccination process sooner, because the two doses must be given at least four weeks apart. Talk to your child's doctor to see if they need one or two doses of flu vaccine.

The body's immune response from vaccination declines over time, so it needs an annual vaccine for the best protection. Flu viruses are constantly changing. The formulation of the flu vaccine is reviewed each year and updated to keep up with changing flu viruses.

No. It takes at least two weeks after vaccination for antibodies to develop in the body and provide protection against an influenza virus infection. That's why it's better to get vaccinated early in the fall, before the flu season really gets under way.

Yes. There is still a possibility you could get the flu even if you got vaccinated.

The flu vaccine's ability to protect a person depends on various factors, including the age and health of the person being vaccinated, and the similarity or “match” between the viruses used to make the vaccine and those circulating in the community. If the viruses in the vaccine and the influenza viruses in the community are closely matched, vaccine effectiveness is higher. If they are not a close match, vaccine effectiveness can be reduced.

Even when the viruses are not closely matched, the vaccine can still protect many people and prevent flu-related complications. Antibodies made in response to the vaccine can provide some protection (called cross-protection) against different but related influenza viruses.

It can vary from year to year and among different age and risk groups. For more information about the flu vaccine, visit the California Department of Public Health's website and the American Academy of Pediatrics' website.

There are many reasons to get a flu vaccine each year. For additional information, please visit the California Department of Public Health's website to learn more.

• Flu vaccines help everyone to stay healthy and protect against illness.
• Flu vaccines lower your chances of illness and hospitalization.
• Flu vaccines lower the risk of serious health problems for:
  • Older adults
  • Infants and children
  • People with chronic health conditions such as asthma, diabetes and heart disease.
• Flu vaccines during pregnancy help protect people who are pregnant and their babies from early delivery, low birth weight and stillbirth.

It's safe and effective to get flu vaccines at the same time as COVID-19, RSV, or other vaccines. Check with your primary care physician if you have questions.