The science behind the flu shot

We’ve all been told how important it is to get vaccinated against the flu every year. But how does the flu vaccination actually work, and why should you get it?

Dr. Steven Green, chief medical officer of Sharp Rees-Stealy Medical Group, shares important information you need to know about the flu vaccine.

What is the flu shot made of?
The flu shot works by exposing an individual to an inactivated form of the influenza virus, aka the “flu.” This exposure can stimulate an immune response that provides protection from the flu without causing illness.

There are many different strains of the flu, and the predominant strains that spread change each flu season. Every year the flu vaccine is reformulated and standardized by the U.S. Public Health Service to include four influenza strains that are predicted to circulate through the community during the upcoming season. So a typical flu vaccine is actually several vaccines rolled up in one, to protect against different strains.

How does the vaccine work?
The vaccines work by inducing specific antibody production, thus promoting immunity to the virus. It takes approximately two weeks after vaccination for the antibodies to develop in the body. While the vaccine will not cause the flu, it is not uncommon that vaccination can cause mild flu-like symptoms.

How effective is it?
Dr. Green advises everyone who is eligible to receive the vaccine to do so if they haven’t already.

“Even though we are not always sure the strains causing the epidemic will exactly match those in the vaccine, the downside is very small,” he says. “If someone is exposed to a strain in the vaccine they received, the infection will be less severe or not even noticeable.”

In addition, the antibodies from each year’s vaccine persist, so if someone gets vaccinated yearly, they will have more antibodies to more strains over time and be less likely to get the flu in future years as well.

Are there alternatives to the flu shot?
The live vaccine (nasal spray vaccine) is an option for healthy, non-pregnant, non-immunocompromised patients 2-49 years old.

Who should get vaccinated?
An annual flu shot is recommended for everyone 6 months of age and older (with rare exception), including pregnant women, people with chronic health conditions and older adults. Some children ages 6 months to 8 years old who are getting vaccinated for the first time will require two doses of flu vaccine spaced at least 28 days apart. Talk to your doctor if you have had a severe allergic reaction to the flu vaccine or any ingredient in the vaccine (including gelatin, antibiotics or other ingredients); have ever had Guillain-Barré syndrome; or are not feeling well prior to receiving the flu shot.

Sharp offers ways to stay protected against the flu. Contact your doctor’s office directly to learn how to get vaccinated. For more information on vaccine availability and vaccination hours at local clinics, visit the San Diego Immunization Branch website or call 211.

This story was updated in November 2018.