Federal health officials have approved the first vaccine that protects against four strains of the common flu, offering one additional layer of protection against the influenza virus that affects millions each year. The FluMist Quadrivalent vaccine from AstraZeneca’s MedImmune unit protects against two strains of influenza A and two strains of influenza B. The Food and Drug Administration approved the spray-based vaccine for people ages 2 to 49. Previously all vaccines contained two strains of influenza A and one strain of influenza B, chosen annually by medical experts based on their potential to spread the virus. Having an extra strain of influenza B increases the likelihood that the vaccine will protect against illness, the FDA said in a statement.
