including H and N from birds; and the H3N2 ‘Hong Kong’ flu of 1968 acquired two new genes from wild ducks. The ‘Russian’ flu of 1977, which probably escaped from a lab in Russia, was a 1950s version of H1N1; whereas the H1N1 ‘swine’ flu which appeared in Mexico in 2009 has six genes from North American and two genes from Eurasian pig flu viruses.
