Seasonal flu shot may increase A/H1N1 risk: studies

The article said four studies, by the Canadian researchers, were carried out in some 2,700 people after an outbreak in April 2009 first signaled a possible connection between seasonal flu vaccine and pandemic flu illness.

Results show that the likelihood of needing medical attention for pandemic flu was 1.4 to 2.5 times greater among people who were vaccinated the previous fall.

In one study, an ongoing sentinel monitoring system was used to assess the frequency of prior vaccination with the seasonal flu vaccine in people diagnosed with A/H1N1 flu in 2009 compared to people without the pandemic flu.

Findings show that seasonal flu vaccination was linked to 68 percent increased risk of getting A/H1N1 flu.

The other studies, including additional case-control investigations and transmission study, reveal that seasonal flu vaccination was associated with a 1.4- to 5.0-times greater risk of having A/H1N1 flu.

However, the authors warn that since all four studies were observational, even careful design cannot rule out the possibility that some undetected methodologic bias affected the results, Kazinform cites Xinhuanet. See www.xinhuanet.com for full version.