2009 swine flu pandemic vaccine

The 2009 swine flu pandemic vaccines were influenza vaccines developed to protect against the pandemic H1N1/09 virus. These vaccines either contained inactivated (killed) influenza virus, or weakened live virus that could not cause influenza. The killed virus was injected, while the live virus was given as a nasal spray. Both these types of vaccine were produced by growing the virus in chicken eggs. Around three billion doses were produced, with delivery in November 2009.

In studies, the vaccine appeared both effective and safe, providing a strong protective immune response and having a similar safety profile to the usual seasonal influenza vaccine. However, about 30% of people already had 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 provided some cross-protection against the 1918 flu pandemic strain.

Early results (pre-25 December 2009) from an observational cohort of 248,000 individuals in Scotland showed the vaccine to be effective at preventing H1N1 influenza (95.0% effectiveness [95% confidence intervals 76.0–100.0%]) and influenza-related hospital admissions (64.7% [95% confidence intervals 12.0–85.8%]).

Developing, testing, and manufacturing sufficient quantities of a vaccine is a process that takes many months. According to Keiji Fukuda of the World Health Organization, "There's much greater vaccine capacity than there was a few years ago, but there is not enough vaccine capacity to instantly make vaccines for the entire world's population for influenza." The nasal mist version of the vaccine started shipping on 1 October 2009.