Influenza vaccine

Influenza vaccines, also known as flu shots, are vaccines that protect against influenza. A new version of the vaccine is developed twice a year as the influenza virus rapidly changes. Most provide modest to high protection against influenza; however, each year this varies. Evidence in adults over 65 years old is poor. They decrease the number of missed days of work by a half day on average. Vaccinating children may protect those around them.

Both the World Health Organization and Centers for Disease Control and Prevention recommends nearly all people over the age of 6 months get the vaccine yearly. This is especially true for pregnant women, children between six months and five years of age, those with other health problems, Native Americans, and those who work in healthcare.

The vaccines are generally safe. In children fever occurs in between 5 to 10%, as may muscle pains or feeling tired. In certain years, the vaccine causes Guillain-Barre syndrome in older people in about one per million doses. It should not be given to those with severe allergies to eggs or to previous versions of the vaccine. The vaccines come in both inactive and weakened viral forms. The inactive version should be used for those who are pregnant. They come in forms that are injected into a muscle, sprayed into the nose, or injected into the middle layer of the skin.