The 2009 flu pandemic vaccines are the set of influenza vaccines that have been developed to protect against the pandemic H1N1/09 virus. These vaccines either contain inactivated (killed) influenza virus, or weakened live virus that cannot cause influenza. The killed vaccine is injected, while the live vaccine is given as a nasal spray. Both these types of vaccine are usually produced by growing the virus in chicken eggs. Around three billion doses will be produced annually, with delivery from November 2009.

In studies, the vaccine appears both effective and safe, providing a strong protective immune response and having similar safety profile to the normal seasonal influenza vaccine. However, about 30% of people already have some immunity to the virus, with the vaccine conferring greatest benefit on young people, since many older people are already immune through exposure to similar viruses in the past. The vaccine also provides some cross-protection against the 1918 flu pandemic strain.

TIV works by putting into the bloodstream those parts of three strains of flu virus that the body uses to create antibodies; while LAIV works by inoculating the body with those same three strains, but in a modified form that cannot cause illness. LAIV is not recommended for individuals under age 2 or over age 49, but might be comparatively more effective among children over age 2.

Figure 1. Massive vaccination of young children during the 2009 flu pandemic.