MicrobeWorld

VACCINATING people against swine flu may be a lot easier than anyone dared hope, as it turns out that people have an unexpected degree of immunity to the pandemic now sweeping the world.

A seasonal flu in the same H1N1 family as the pandemic virus has been circulating since 1977, but until now it was thought that this seasonal virus did not induce immunity to the pandemic strain. This was because the pandemic virus spread faster than would be expected if there were widespread immunity to it, and because antibodies to the seasonal vaccine do not cross-react with it.