A viral mystery: Can one infection prevent another?

In September 2009, the H1N1 swine flu had arrived in Portugal, Spain, and the UK, so France braced itself for cases of the infection.
Indeed, the number of people in France with respiratory symptoms soon increased. But they did not seem to have H1N1. France registered only sporadic positive tests for the new swine flu for most of that September and the first half of October. When H1N1 finally took hold in France, it was much later in the fall than expected. And that got scientists thinking: Why? Read the rest…