XK and influenza: Studies have shown that H3N2 influenza in Hong Kong in 1968 was also due to recombination with the human H2N2 virus NA, PB2, PA, NP, M and NS genes, but the population does not have immunity to the new HA and NA, resulting in the rapid spread of the new virus, causing a human flu pandemic (Lindstrom et al., 2004).