Swine Flu XIII: Seasonal flu shot may increase H1N1 risk

Preliminary research suggests the seasonal flu shot may put people at greater risk for getting swine flu, CBC News has learned.

 

"This is some evidence that has been floated. It hasn't been validated yet, it's very preliminary," cautioned Dr. Don Low, microbiologist-in-chief at Mount Sinai Hospital in Toronto.

 

…Four Canadian studies involved about 2,000 people, health officials told CBC News. Researchers found people who had received the seasonal flu vaccine in the past were more likely to get sick with the H1N1 virus.

 

Researchers know that, theoretically, when people are exposed to bacteria or a virus, it can stimulate the immune system to create antibodies that facilitate the entry of another strain of the virus or disease. Dengue fever is one example, Low said.

 

The latest finding raises questions about the order in which to get flu shots.

 

…The main reason is that H1N1 may be the dominant strain of influenza circulating when the fall flu season hits, meaning it could be a waste of time and resources to mount a seasonal flu vaccine campaign.

 

"We don't know with this year's flu shot how it interacts with the pandemic flu shot, so it's a worry," said Dr. Michael Gardam, director of infectious diseases prevention and control at the Ontario Agency for Health Protection and Promotion.

 

CBC News, September 23, 2009