There are, appropriately, public health concerns with any new strain of influenza that develops. During the last century we have had three major events where millions of people died after new strains (H1, H2 and H3) spread to people and to which we had little or no pre-existing immunity (eg H1N1 Spanish Flu from 1918-19). These new strains spread to people from strains derived from birds, often after mixing their genetic components in pigs. This latter mixing made them more adept at spreading from person to person. The current "Swine flu" strain has a mix of human, pig and bird genetic components and thus is of some concern.

However this current strain does not fulfil two essential characteristics needed for any Flu strain to be the same problem as Spanish flu. For any Flu strain to be a problem of the same magnitude it needs: to readily spread from person to person AND to have a more aggressive (or virulent) effect in people compared to the strains that are circulating now and causing problems every winter.