Does a seasonal flu shot raise the risk of swine flu?

By Dr. Ananya Mandal, MDApr 7 2010

Four new studies by Canadian researchers have come up with the result that the traditional seasonal flu vaccine that has been used for some time now is related to an increased risk of infection with pandemic H1N1 swine flu.

One of the studies involved an ongoing monitoring system to assess the frequency of prior vaccination with seasonal flu vaccine and among people diagnosed with swine flu in the 2009 pandemic. The results showed a staggering 68% increased risk of getting swine flu among the vaccinated people.

The other 3 studies included investigations of similar nature in Ontario and Quebec – areas hit with swine flu. In all these studies 1.4 to 5 times higher risk of getting swine flu was seen in seasonal flu vaccinated individuals. These studies have been published in the April 6^th issue of PLoS Medicine, an online journal. Principal investigator Danuta Skowronski, of the British Columbia Center for Disease Control in Vancouver however said that there may be an underlying common susceptibility that is the reason for this finding. The actual association between the two is still uncertain. However the biological interaction between the two strains of influenza virus cannot be denied completely.