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Seasonal Vaccine

What Is The Seasonal Flu Vaccine?

Influenza is more than a nuisance. It’s a virus that can prove deadly, especially to young people and the elderly. According to the World Health Organization (WHO), an estimated 250,000 to 500,000 people die annually from the flu across the world.

The seasonal flu vaccine is a way for people ages 6 months and older to protect themselves against the flu. According to WHO, healthcare providers have administered the flu vaccine for more than 60 years. Because there is no cure for the flu, the flu vaccine can protect you from getting the flu or make flu symptoms less severe.

A new flu vaccine is manufactured each year when WHO and other infection-prevention organizations make recommendations regarding the types of inactivated flu viruses that should be included in the vaccine. These viruses are traditionally grown in hens’ eggs and harvested to make the vaccine.

When you get the flu vaccine, your body starts to build up antibodies or protective immune cells against the virus. If you are exposed to the flu virus, your body will make the antibodies faster to beat the virus.

What Flu Vaccine Types Are Available?

Two flu vaccine types that exist are trivalent and quadrivalent. The trivalent vaccine protects against three flu virus strains. The 2014-2015 vaccine contained inactivated strains of A/H3N2, A/H1N1 and influenza B. Quadrivalent vaccines protect against the same strains as the trivalent, plus an additional strain. The 2014-2015 vaccine included an additional influenza B strain.

In addition to traditional formats, trivalent vaccines are available as high-dose flu shots for those ages 65 and older. They can stimulate a stronger immune system response, better protecting seniors against the flu. Recombinant shots or cell-based vaccines are given to people ages 18 and older allergic to eggs that cannot get the traditional flu vaccine.

Healthcare providers administer the flu vaccine in a variety of forms. These include:

  • Intramuscular (IM) shot: This shot is given into the shoulder muscle and is the traditional site for flu injections. Anyone 6 months of age and older can receive this flu shot type.
  • Subcutaneous shot: This shot uses a shorter needle that does not penetrate to the muscle. Those ages 18 to 64 can receive this short type.
  • Nasal spray: This inhaled form of the vaccine is approved for healthy people ages 2 to 49. Pregnant women cannot get this flu vaccine form, however.

Quadrivalent vaccines are only available as traditional IM shots and nasal sprays.

According to the Centers for Disease Control and Prevention (CDC), children between the ages of 2 and 8 should get the nasal spray, as long as the child is healthy and has no indications why they shouldn’t get the vaccine. The CDC does not list any other preferences for vaccine administration.

Who Should Get the Flu Vaccine?

The Advisory Committee on Immunization Practices (AICP) recommends all people ages 6 months and older should have the flu vaccination unless they have a contraindication that would keep them from safely getting the vaccine. According to WHO, people who should get the flu vaccine due to their increased risk for getting or spreading the flu include:

  • pregnant women
  • the elderly
  • children ranging from 6 months to age 5
  • those with chronic medical conditions
  • healthcare workers

Some people shouldn’t get the traditional flu vaccine. Healthcare providers are required to screen patients for these exclusions to minimize risk for allergic reactions. People who should not get the traditional flu vaccine include:

  • those who have had a severe or life-threatening reaction to the flu vaccine in the past
  • those who are allergic to any part of the vaccine, including gelatin, antibiotics, or eggs
  • those with a history of Guillain-Barré Syndrome
  • those with a mild illness and are not feeling well or who have a fever

Talk to your healthcare provider about alternative options for the flu vaccine.

When Should the Vaccine Be Administered?

According to the CDC, flu vaccines take roughly two weeks to provide immunity. After you get your flu shot, your body starts developing infection-fighting antibodies that prevent the flu. According to, you should get the flu vaccine as soon as it’s available at your physician’s office, health department, or other healthcare facility. It usually becomes available in October, and flu season tends to begin in January or February.

While there may be a better time for flu vaccine administration, getting the vaccine at any time can offer protection. Because flu season can last until May, it’s rarely ever too late to have your flu shot.

Note the flu vaccine will only last for one flu season at a time. You will need to get another flu vaccine when the next flu season comes around.

What Are the Flu Vaccine’s Side Effects?

The flu vaccine can cause symptoms that range from mild to moderate. According to the CDC, the risk for serious injury or death is possible, but very remote for the flu vaccine. The occurrence of a severe allergic reaction is less than 1 in 1 million. Severe reactions typically occur within minutes of receiving the vaccine. Severe allergic reaction symptoms include:

  • dizziness
  • facial swelling
  • hives
  • rapid heartbeat
  • weakness

Mild flu symptoms include:

  • body aches
  • cough
  • headache
  • fatigue
  • fever
  • itching
  • redness, swelling, or soreness at the injection site
  • sore, red, or itchy eyes

Moderate side effects can occur if young children get the flu vaccine and the pneumococcal vaccine (PCV13) at the same visit. A fever that triggers seizures can occur.

It’s a myth that you can get the flu from the flu vaccine. The flu vaccine contains inactivated flu viruses. Because the viruses are not "live," they cannot cause the flu. 

How Effective Is the Vaccine?

While the flu vaccine does not protect against all flu types, it does make you less likely to get the flu. According to, you are 60 percent less likely to require flu treatment from a healthcare provider if you get the flu shot.

According to the CDC, getting the flu vaccine reduces:

  • flu-related hospitalizations for adults by 74 percent
  • hospitalizations in people with diabetes by 79 percent and chronic lung diseases by 52 percent
  • the risk for flu-related hospitalizations in people ages 50 and older by 61 percent

The flu vaccine is researchers’ best guess at what flu viruses will circulate in a given year. Some years prove more effective than others in flu prevention.

What Are the Safety Considerations for the Flu Vaccine?

While there is always potential for an allergic reaction to the flu vaccine, the vaccine is largely considered safe. According to, the CDC and the U.S. Food & Drug Administration closely monitor the flu vaccine’s safety to ensure the vaccine doesn’t have unintended ill effects. 

Content licensed from:

Written by: Rachel Nall
Medically reviewed on: Nov 24, 2014: George Krucik, MD, MBA

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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