When is flu season?

The flu season [2] can start as early as October and late as late as May, but typically peaks between December and February.

What does the flu shot do?

Flu vaccines cause antibodies to develop [3] in the body about two weeks after the vaccination is administered and provide protection against infection from those strains of the virus included in the vaccine.

Are there different types of flu shots?

There are many different types of flu shots — some in higher doses than others — but a few of the most common include:

• Trivalent flu shot, designed to protect against three different flu strains (two influenza A strains, one influenza B strain) using a killed version of the virus [4].
• Quadrivalent flu shot, designed to protect against four different flu strains (two influenza A strains and two influenza B strains) using a killed version of the virus.
• Quadrivalent nasal spray vaccine, designed to protect against four flu strains (two influenza A strains and two influenza B strains) using a live virus.

How old should you be to receive a flu shot?

Not all flu shots [5] are created equal in terms of how old you should be to receive one.

• Standard-dose trivalent shots: Each version is different, but some are approved for those as young as 6 months.
• A trivalent shot containing virus grown in cell culture: Ages 18 and over
• A recombinant trivalent shot that is egg-free: Ages 18 and over
• Quadrivalent flu shot: Each version is different, but some are approved for those as young as 6 months.
• Quadrivalent nasal spray vaccine: Ages 2 through 49

Who cannot get a flu shot?

Those who should not get a flu shot include:

• Anyone younger than 6 months old
• People with life-threatening allergies to ingredients in the shots, which could include gelatin, eggs, or antibiotics
• Any child aged 6 months to 18 years who has ever had a severe allergic reaction to eggs — they should not get a flu shot until the age of 18, when they can get a recombinant (egg-free) flu vaccine.

Who cannot get the nasal spray vaccine (FluMist)?

Those who should not get the nasal spray vaccine include:

• Children younger than 2 years old
• Children 2 years through 17 years of age who are receiving aspirin therapy or aspirin-containing therapy
• Children 2 through 4 years old who have asthma or who have had a history of wheezing in the past 12 months
• Anyone who is allergic to eggs
• Pregnant women, though they need not avoid contact with anyone who has gotten the nasal vaccine

What are the side effects of flu shots?

Side effects of the shot [6] may include:

• Sore, red, or swollen injection site
• Low-grade fever for a few days afterward
• Muscle aches

Side effects of the nasal spray in children:

• Runny nose
• Wheezing
• Headache
• Vomiting
• Muscle aches
• Fever

Side effects of the nasal spray in adults:

• Runny nose
• Headache
• Sore throat
• Cough

What are the benefits of the flu shot?

In general, the risks associated [7] with the actual flu virus — severe, long-lasting symptoms; pneumonia; bacterial infections; and even hospitalizations — are much worse [8] than the risks of the shot.

Bear in mind also that vaccinations don't just prevent you from getting sick — by getting a flu shot, you are not only reducing your own chances of contracting the flu, but are also keeping those around you from getting sick as a result (especially babies under 6 months old who cannot receive the shot and have a weaker immune system).

Always consult your doctor if you are unsure what to do.