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Is the H1N1 Swine Flu Vaccine Safe?

H1N1 Swine Flu Vaccine Safety: Hype, Myths, and Facts

Does the H1N1 swine flu vaccine contain thimerosal?

The 2009 H1N1 swine flu vaccine comes in three basic types: the FluMist nasal spray, single-syringe shots, and multi-shot vials.

Only the multi-shot vials contain thimerosal, a preservative that prevents bacterial contamination of the vial. Before thimerosal was added to vaccines, there were occasional vaccine injuries due to contamination.

Extensive study shows that there are no more adverse events in children or adults who receive thimerosal-containing vaccines than in those who do not.

But thimerosal contains a form of mercury. It's ethyl mercury, which is likely not as toxic as some other forms. Even so, nobody argues that mercury is good for your body. People who want to avoid thimerosal-containing flu vaccines must get the FluMist vaccine or the single-syringe shots.

Most people should have this choice. But single-syringe vaccines may not be available for every person in every location during every week of the vaccination campaign.

The 1976 swine flu vaccine wasn't safe. Why should I trust this one?

The 1976 swine flu vaccine was linked to safety issues. Neal Halsey, MD, director of the Institute for Vaccine Safety at the Johns Hopkins Bloomberg School of Public Health, was at the CDC in those days.

"We did identify an increased risk of GBS [Guillain-Barre syndrome] in the six weeks following immunization," Halsey tells WebMD. "What is not known at this time is exactly why that vaccine was associated with that increased risk."

No flu vaccine since then has been linked to this risk. Halsey thinks there is the potential for the H1N1 flu vaccine to carry a risk of causing one case of GBS per million people vaccinated.

"The theoretical risk of that rare complication has to be balanced against the severity of the H1N1 flu," he says. "There already have been a lot of deaths, many in otherwise healthy, normal children. There is always a real risk from the flu, and a theoretical risk from the vaccines."

In 1976, the risk from flu was theoretical, too. Despite a scary and fatal outbreak of an H1N1 swine flu at a military base, the virus never spread.

The 1976 H1N1 swine flu was a very different virus from the 2009 H1N1 swine flu, which combines elements from flu viruses that evolved in birds, humans, and pigs. And unlike the 1976 virus, the 2009 bug is causing a very real pandemic.

Do we really know what drugmakers are putting in the swine flu vaccine?

Vaccine labels are not easy to read. But they are made public by the FDA and other sources. If you want to know exactly what's in each kind of 2009 H1N1 swine flu vaccine, read the label. You can find all the labels here: http://www.vaccinesafety.edu/package_inserts.htm.

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Reviewed on October 14, 2009

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