We need a flu shot annually because influenza virus changes structure and shape as it moves around the globe each year. The strains that cause human disease are different from one year to the next, so we update and add to our protection annually by getting a shot or nasal flu spray. Children, especially those under age 5, are at higher risk for severe disease from influenza. In children and adults, influenza can cause a mild illness, but unfortunately, sometimes it can cause severe or even life-threatening complications. Children may have a more difficult time fighting off influenza partly because they don’t have years of exposure to other strains of flu and no real immunity built up. Therefore all children are considered a priority group for flu shots. Pregnant women, families with infants at home, and those with underlying medical problems like asthma, diabetes, or neurologic problems really need to get them, too.
It takes a well-orchestrated, worldwide effort to help predict which strains come to our country and which 3 strains are included in the annual flu shot or flu nasal spray here in The United States. The video explains more.
Every Year Is An Influenza Pandemic For Children (commentary)