In March and early April 2009, a new swine -origin influenza A ( H1N1 ) virus (S-OIV) emerged in Mexico and the United States1. During the first few weeks of surveillance, the virus spread worldwide to 30 countries (as of May 11) by … This virus has the potential to develop into the first influenza pandemic of the twenty-first century. [I thought a pandemic alert level of 6 meant it had already?? - Ed] Here we use evolutionary analysis to estimate the timescale of the …
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Where the new H1N1 came from « ViroBlogy