Which of the following statements about influenza vaccines and avian strains is correct?

• A. They prevent all avian strains
• B. They may provide partial protection against some avian strains
• C. They have no impact on avian strains
• D. They are only used for birds

Answer: (B)

Influenza vaccines are designed to protect against the strains circulating in humans during a given season, not to cover every bird-origin virus. Because avian strains can be quite different from the human vaccine strains, these vaccines do not prevent all avian strains. However, if an avian strain shares similar features with the vaccine strains, the immune response elicited by the vaccine can cross-react and provide partial protection against those particular avian strains. The level of protection depends on how closely the avian strain resembles the vaccine strains and the person’s immune history. So, partial protection against some avian strains is possible, rather than universal protection or no impact; and these vaccines are not used only for birds.