Expect yearly visits from swine flu’s cousins
How long will immunity last, after H1N1 vaccination, or after natural infection? F. Foley, MD, Toronto, ON
Because the swine origin H1N1 influenza strain is a novel strain, and since we’ve had only a recent experience with the new H1N1 vaccines, any answer must be somewhat speculative. Both immunization and natural infection result in high levels of antibody. Protection from that exact strain of influenza may be expected to be quite high for years in healthy people. However, the influenza virus has a remarkable ability to mutate. Minor mutations (“drift”) in the virus will allow it to infect previously infected or vaccinated individuals. But when that does happen, this illness will generally be much milder and associated with far fewer complications that in individuals who haven’t had previous immunity. History suggests that mutated versions of the swine origin H1N1 virus of 2009 will likely become one of the seasonal influenza viruses for which new vaccine formulations will be required annually.