The CDC’s new H1N1 data re-emphasize that, compared to seasonal flu, swine flu has disproportionately affected people under 65. Vincent Racaniello, a professor of microbiology at Columbia University, recently summarized a study done in mice that suggests one possible reason for this. The study appears to confirm initial hunches that many older people have immunity to swine flu because of previous H1N1 vaccines or bouts of flu.
The mice, Racaniello says, were inoculated with various past strains of H1N1 — and it turns out that several of those strains offered significant protection:
In other words, if you lived before 1943, or received the 1976 swine flu vaccine, you may be protected against infection with 2009 H1N1 virus. After the 1976 swine H1N1 outbreak at Fort Dix, NJ, approximately 40 million people in the United States were immunized with an NJ/76 vaccine. The NJ/76 swine virus never spread in the general population, but the vaccine against it has finally proven useful.
If you are less than 35 years old, you are more likely to be infected with the 2009 H1N1 virus because you did not receive the NJ/76 vaccine, nor were you infected with viruses that circulated from 1918-1943.
Racaniello blogs regularly at Virology Blog. You can find his previous posts exploring the same topic here, here, and here. The mouse study that Racaniello cites is here.
