Due the frightening outcome of the related strain, US public health officials quickly developed huge amounts of a vaccine to the new strain. Even though some people chose not to be vaccinated, there was no epidemic the following flu season. A very rare association with the new flu vaccine was Guillain Barre Syndrome. This serious condition caused paralysis. Therefore, because of highly visible side effects, and no visible proof that the vaccination program actually avoided an epidemic, public health officials were criticized rather than rewarded for their quick response.
Orthomyxoviruses sometimes make red blood cells stick together.
Two different strains must infect the same host. The virus also must be promiscuous. Influenza A exhibits antigenic shift every 10 to 40 years. Shift is one reaon why the virus can spread throughout the world so quickly. They occur within one subtype.