What it prevents: H1N1, also called the swine flu, is a relatively new strain of the influenza virus. Symptoms of the swine flu are pretty much the same as regular flu – coughing, sneezing, fever, sore throat, and achiness. (And like regular flu, H1N1 can occasionally cause pneumonia and death). The swine flu caused panic when it quickly surfaced and became widespread in 2009 since a new strain means no one in the population has immunity, and it can spread fast. Despite fears, however, it mostly ended up acting like regular old flu. And immunity among the general population is now increased through immunizations and antibodies developed after contracting it.

When and how it’s given: Children under nine should receive two doses of the H1N1 vaccine, each about a month apart, at the start of the flu season. Children older than nine can receive just one dose. Children should be vaccinated against H1N1 starting at 6 months of age. Once your child is two, he may be eligible to receive the nasal spray vaccination, assuming that he doesn’t have asthma and isn’t prone to episodes of wheezing when he’s sick. (If he does, he may be eligible for the flu spray after he turns five.)

Like the flu vaccine, there are two types of flu immunization; an inactivated version (given by injection) and a live version of the vaccine, which contains a weakened, but real form of the flu virus (given as a nasal spray).

What you may have heard: The swine flu vaccine was in short supply in 2009, the first year it was available, and it was hard to get advice on whether to get one for your child even if you got your hands on it. In 2010, the CDC added it to the regular vaccine schedule. Some H1N1 shots still use thimerosal as a preservative. If you’re concerned about this, you can ask your doctor about receiving a thimerosal-free version of the H1N1 shot. The nasal spray does not contain thimerosal.

Risk of reaction: Like the flu virus, the H1N1 vaccine is grown in eggs. Children with a severe egg allergy generally do not receive a flu shot. If your child has an allergy to eggs (or you have a family history of egg allergy), talk to your doctor. Mild side effects of the injection include redness, soreness and swelling at the injection site as well as a mild cold symptoms (cough, fever, aches) that can last one to two days. Mild side effects of the spray include flu-like symptoms such as a cough, runny nose, fever, wheezing or upset stomach.