Feature Archive

Is the H1N1 Swine Flu Vaccine Safe?

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

By Daniel J. DeNoon
WebMD Feature

Reviewed by Louise Chang, MD

What do we really know about the 2009 H1N1 swine flu vaccine? What do we really not know?

Questions about the safety of the vaccine persist. Surf the Internet or flip through TV stations and you'll encounter a multitude of myths and a whole lot of hype.

What are the facts? Straightforward answers follow these questions:

  • Is the 2009 H1N1 swine flu vaccine safe?
  • Isn't the 2009 H1N1 swine flu vaccine too new to trust?
  • Why should I believe what government scientists say about swine flu?
  • Does the H1N1 swine flu vaccine contain thimerosal?
  • The 1976 swine flu vaccine wasn't safe. Why should I trust this one?
  • Do we really know what drugmakers are putting in the swine flu vaccine?

Is the 2009 H1N1 swine flu vaccine safe?

No vaccine is 100% safe for everyone. People with allergies to eggs, for example, can't take flu vaccines because eggs are involved in the manufacturing process.

And flu vaccines cause mild but common reactions. About one in three people get a sore arm from the shot, some with a little redness or even swelling. Some 10% to 15% of people feel tired or get a headache; some may even run a low fever.

And vaccines can trigger rare but serious reactions, even among people with no apparent allergies or sensitivities.

So if vaccines aren't 100% safe, why risk them?

Approved vaccines -- including the 2009 H1N1 swine flu vaccine -- are calculated to be much, much less risky than the diseases they prevent. For example, out of every million people who get a flu shot, one or two will get a serious neurological reaction called Guillain-Barre syndrome (GBS).

But flu itself causes serious problems, including GBS, in far more than two in a million cases. And since a large proportion of the population will get swine flu, the vaccine risk is far smaller than the disease risk.

In clinical trials, 10,000 to 15,000 children and adults have received various manufacturers' brands of H1N1 swine flu vaccine. Nothing serious happened to any of them, including this reporter, who received a double dose of the Sanofi-Pasteur swine flu vaccine.

That's still not proof that no harm will come from the vaccine. Clinical trials cannot detect something bad that happens to one or two out of every 100,000 people vaccinated.

"There could be unknown side effects. Something could happen. But we think that is highly unlikely," says infectious disease and vaccine expert Mark Mulligan, MD, executive director of the Hope Clinic of the Emory Vaccine Center in Atlanta.

"The CDC, FDA, HHS [Health and Human Services Department], the Department of Defense, and several large HMOs with great medical records are all collaborating in enhanced surveillance for this national 2009 H1N1 vaccine campaign," Mulligan tells WebMD. "If there is a signal for a rare or late adverse event, we will identify it as early and as quickly as we can."

Isn't the 2009 H1N1 swine flu vaccine too new to trust?

Is the swine flu vaccine brand new? Yes and no. The 2009 H1N1 swine flu vaccine is made exactly the same way as the seasonal flu vaccine, by the same manufacturers using the same materials -- except for one shiny new piece.

What has changed is the piece of the virus the vaccine uses to prime the immune system.

Vaccine experts tell WebMD this change isn't all that new. Every couple of years or so, a new variant of a seasonal flu virus comes along. When that happens, a "new" vaccine is made using the relevant part of the variant virus.

And even though the 2009 H1N1 swine flu is a genuinely new virus, it's still closely related to seasonal flu bugs. One of the vaccines in the three-in-one seasonal flu vaccine protects against seasonal H1N1 flu, which is about 75% similar to the 2009 H1N1 swine flu -- although it offers no protection against the pandemic flu.



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