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Sharp Health News

The science behind the flu shot

Oct. 23, 2015

The flu shot

Flu season has officially begun, and we’ve all been told how important it is to get vaccinated against the flu every year. But how does it actually work?

Lindsay Schimpf, infection preventionist at Sharp Coronado Hospital, shares the science behind the flu shot.

What is the flu shot made of?
The flu shot works by exposing an individual to an inactivated or weakened 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 to include three or four influenza strains that are predicted to circulate through the community. 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. The vaccine formula is standardized each year by the U.S. Public Health Service, based on research of the most common viruses during the upcoming season.

Are there alternatives to the flu shot?
Most vaccines are given by injection into the muscle, but some vaccines can be given via nasal spray*. This nasal vaccine is made with a live, but weakened virus, and can only be given to those between 2 and 50 years of age with healthy immune systems. Pregnant women or people who have egg allergies should not receive the nasal spray vaccine. Both live and inactive vaccines will not cause the flu, though it is not uncommon that vaccination can cause mild flu-like symptoms.

What is the difference between injectable and nasal flu vaccines?
Both induce the body to produce antibodies against the influenza virus. But of all the FDA-approved vaccines, only the nasal spray flu vaccine uses the live virus. The vaccine is produced in embryonated chicken eggs and approved for healthy, non-pregnant adults up to 49 years of age. All injectable flu vaccines are prepared from killed virus.

Updated December 7, 2016.

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