Influenza — what most of us call "the flu" — is a highly contagious viral infection of the respiratory tract.

Immunization Schedule

Flu season runs from October to May. It's best to get a flu shot early in the season, as it gives the body a chance to build up immunity to (protection from) the flu. But getting a flu shot later in the season is still better than not getting the vaccine at all.

The Centers for Disease Control and Prevention (CDC) now recommends a flu vaccine for everyone 6 months of age and older (instead of just certain groups, as was recommended before). But it's especially important that those in higher-risk groups get vaccinated. They include:

• all kids 6 months through 4 years old
• anyone 65 years and older
• women who will be pregnant during flu season
• anyone whose immune system is weakened from medications or illnesses (like HIV infection)
• residents of long-term care facilities, such as nursing homes
• any adult or child with chronic medical conditions, such as asthma
• kids or teens who take aspirin regularly and are at risk for developing Reye syndrome if they get the flu
• health care personnel who have direct contact with patients
• Native Americans and Alaskan natives
• caregivers or household contacts of anyone in a high-risk group

Infants younger than 6 months can't get the vaccine, but if the parents and older kids in the household get it, that will help protect the baby. This is important because infants are more at risk for serious complications from the flu.

• Kids under 9 years old who are getting the flu shot for the first time will receive two separate shots at least a month apart.
• Those under 9 who have received the flu vaccine before still might need two doses if they did not receive at least two vaccines since July 2010, or if the number of shots they've received since then is unknown. This is to ensure that all kids are vaccinated against the H1N1 flu strain that surfaced in 2009.
• Kids older than 9 years old need only one dose of the vaccine.

Talk to your doctor about how many doses your child needs.

A non-shot option, the nasal mist vaccine, is approved for use in healthy 2- to 49-year-olds. It contains live but weakened virus that will not cause the flu. However, the vaccine it isn't recommended for kids with certain medical conditions or pregnant women.

In the past, there have been vaccine shortages and delays. So talk with your doctor about availability, and about which vaccine is right for your kids.

Why the Vaccine Is Recommended

While the flu vaccine isn't 100% effective, it still greatly reduces a person's chances of catching the flu, which can be very serious, and can make symptoms less severe if someone does still get the flu after immunization.

Even if you or your kids got the seasonal flu vaccine last year, that won't protect you from getting the flu this year, because flu viruses constantly change. That's why the vaccine is updated each year to include the most current strains of the virus.

Possible Risks

Usually given as an injection in the upper arm, the flu shot contains killed flu viruses that will not cause someone to get the flu, but can cause mild side effects like soreness, redness, or swelling at the injection site. A low-grade fever and aches are also possible.

The nasal spray flu vaccine contains weakened live flu viruses, so it may cause mild flu-like symptoms, including runny nose, headache, vomiting, muscle aches, and fever. Very rarely, the flu vaccine can cause a severe allergic reaction.

When to Delay or Avoid Immunization

Certain circumstances would prevent a person from getting the flu shot. Talk to your doctor to see if a flu shot is recommended if your child falls into any of these groups:

• infants under 6 months old
• anyone who's ever had a severe reaction to a flu vaccination
• anyone with Guillain-Barré syndrome (a rare condition that affects the immune system and nerves)

In the past, it was recommended that anyone with an egg allergy talk to a doctor about whether receiving the flu vaccine was safe because it is grown inside eggs. But health experts now say that the amount of egg allergen in the vaccine is so tiny that it (but not the nasal mist) is safe even for kids with a severe egg allergy. This is especially important during a severe flu season, such as the current one, which started earlier and has been much worse than in years past.

Still, if your child has an egg allergy, he or she should get the flu shot in a doctor's office, not at a supermarket, drugstore, or other venue. And if the allergy is severe, it might need to be given in an allergist's office.

If your child is sick and has a fever, talk to your doctor about rescheduling the flu shot.

Caring for Your Child After Immunization

Pain and fever may be treated with acetaminophen or ibuprofen. Check with your doctor to see if you can give either medication and to find out the appropriate dose.

A warm, damp cloth or a heating pad at the injection site also may help minimize soreness. Moving or using the limb that has received the injection often reduces the soreness as well.

When to Call the Doctor

• Call if you aren't sure if the vaccine should be postponed or avoided.
• Call if there are serious problems after the immunization, such as an allergic reaction or high fever, or if you have other concerns.

Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: January 2013