Safety and Protectiveness of the Seasonal Influenza Vaccine for 2010-2011

The seasonal influenza vaccination program for 2010-2011 will be the first to follow the H1N1 pandemic of 2009. Many Canadians either had the H1N1 infection or the adjuvanted H1N1 vaccine. Both H1N1 infection and adjuvanted vaccine produced strong immune responses which could last for some time. The seasonal influenza vaccine for this fall will be a "normal" product once again, without adjuvant. It will contain 3 strains of killed, split-apart viruses that might circulate this winter, including the H1N1 pandemic strain. It is theoretically possible that giving the H1N1-containing seasonal vaccine to people who still have some immunity to H1N1 virus could result in more frequent side-effects. However, there is no good evidence that pre-existing immunity to a strain in the vaccine does increase side-effects. In short, there could be nothing out of the ordinary this fall but it would be prudent to check this before public flu vaccination programs begin.