a primary reason for needing a new vaccine for influenza each year is that
Influenza vaccine Influenza vaccines, also known as flu shots or flu jabs, are vaccines that protect against infection by Influenza viruses.[2] A new version of the vaccine is developed twice a year, as the Influenza virus rapidly changes.[2] While their effectiveness varies from year to year, most provide modest to high protection against influenza.[2][3] The CDC estimates that vaccination against influenza reduces sickness, medical visits, hospitalizations, and deaths.[4] When an immunized worker does catch the flu, they are on average back at work a half day sooner.[5] Vaccine effectiveness in those under two years old and over 65 years old remains unknown due to the low quality of the research.[6][7][needs update][8][needs update] Vaccinating children may protect those around them.[2]