Epidemiologists in British Columbia find that people who have been vaccinated against the seasonal flu are more at risk to contract the H1N1 virus.
However, study authors remain cautious and say it is too early to establish a clear link. Further studies are needed to validate or invalidate these data.
According to the journal PLoS Medicine, in the spring of 2009, Dr. Danuta Skowronski and colleagues at the BC Centre for Disease Control noticed that several students at one school exhibited H1N1 symptoms. It turns out that the majority of them had been vaccinated against the seasonal flu.
Researchers recruited a total of 2,700 people in British Columbia, Alberta, Ontario and Quebec who participated in four studies. All four studies had similar results and confirm that people who were vaccinated against seasonal flu were protected against it, but were also 68% more likely to be contaminated with H1N1. However, the risk of hospitalization does not change.
However, researchers were quick to point out that it is premature to conclude "that seasonal flu vaccinations increased the risk of pandemic illness in 2009."