Influenza Vaccine

Influenza vaccines, colloquially known as flu shots, are vaccines that protect against infection by influenza viruses, with new versions developed twice a year as the virus rapidly changes. Vaccination against influenza began in the 1930s, with large-scale availability in the United States beginning in 1945, and the World Health Organization and the US Centers for Disease Control and Prevention recommend yearly vaccination for nearly all people over six months of age. The vaccines come in inactivated and live weakened viral forms and can be given by injection into a muscle, sprayed into the nose, or injected into the skin, depending on the type; the live weakened vaccine is generally not recommended for pregnant women, young children, older adults, or those with a weakened immune system. It is on the World Health Organization's List of Essential Medicines.