What strains of influenza does the flu shot protect against?

The flu shot is a single injection that combines three strains of influenza. A new flu vaccine is made every year. When creating a new flu vaccine, researchers pick strains of influenza based on what influenza viruses are likely to be circulating during that year's flu season. The vaccine offers you protection against those three strains.
Diana K. Blythe, MD
The flu shot can be combined with other vaccines. In fact, when getting your flu shot, it is a good idea to check if you are behind on any booster vaccines, whether adult or child. The only thing you have to consider, is if you get the nasal spray version rather than the shot. Since the nasal spray is a live version, it cannot be given within a month of another live vaccine.

The influenza ( flu shot) vaccine is recommended annually in the United States during the fall and winter season to protect against the outbreak of the A, the B, and the H1N1 virus. The vaccine is given in a single dose injection and should not be mixed with any other medicine.

This vaccine is recommended for people that are at a high risk of complications if they become infected with the flu virus. These individuals that are at a higher risk are: 

  • Anyone 65 or older
  • People with chronic lung, heart, liver, or kidney disease
  • Those people that are immunosuppressed ( with HIV, on long term steroids, or receiving chemotherapy treatments) and the people that live with or care for them
  • All healthcare workers
  • Pregnant women and children 6 months of age to 2 years ( may be recommended up to 5 years)
  • People who live in close quarters ( prisons, dormitories, nursing homes, and boarding schools)

The side effects of the flu shot are soreness at the site, slight runny nose, low grade fever, and minor body aches. These symptoms may begin soon after the injection and may last 1-2 days

The flu vaccine is contraindicated if the patient is allergic to eggs, had a severe reaction to the influenza vaccine in the past, or has a history of Guilllian-Barre

If the person has an illness with a fever, they should wait till they recover to get vaccinated.


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Vaccines work to protect your body against germs. Because of vaccines, many of the diseases that can cause severe sickness, handicaps and death have been eradicated. Learn more from our experts about vaccines.

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.