Flu shot ingredients and how they are manufactured
There are 16 different flu shots approved by the FDA, made by several pharmaceutical companies. Some of these vaccines are designed solely to protect against the H1N1 influenza virus A strain. But most flu vaccines distributed in the U.S. are designed to provide protection from three strains of influenza viruses: two strains of type A influenza viruses, and one strain of type B influenza virus. The strains are chosen every year by the World Health Organization and the Centers for Disease Control, based on a best guess as to the greatest threat in any given year.