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H1N1 (swine) flu is in the news again (courtesy of flickr user Dr Craig)

Around the country, people are lining up to be vaccinated against the H1N1 flu virus. Surprising Science has spent the last three days discussing the history and science of vaccines (see A Brief History and How Vaccines Work, Success Stories, and A History of Vaccine Backlash). Today we answer some of the more common questions about the swine flu vaccine.

Who should get the H1N1 flu vaccine?

There is currently not enough vaccine for everyone who wants it. Vaccines take time to produce and this one has been rolling off the line for just a few weeks. As of Tuesday there were about 22.4 million doses available around the United States. The goal is to have 250 million doses by the end of flu season next spring. The Centers for Disease Control and Prevention have recommended that certain groups get vaccinated first:

• pregnant women
• people who live with or care for children under six months of age
• young people age six months to 24 years
• people 25 to 64 who are at higher risk for flu complications due to a health condition or compromised immune system
• health care and emergency medical service personnel

Why are these groups first?

Pregnant women and young people seem to be especially vulnerable to the H1N1 virus. Babies under six months of age cannot be vaccinated, so it is important to limit their exposure to the virus by vaccinating people who care for them. People with certain health conditions or who have a compromised immune system have a higher risk of having serious flu complications if they get the flu. And medical personnel are the people most likely to come in contact with the virus.

What if I’m not in one of these groups?

Wait your turn. There will be enough vaccine eventually. And if you get the H1N1 flu, it won’t be fun but also probably won’t do you long-term harm. In the meantime, the CDC recommends taking everyday preventative actions like hand washing and avoiding contact with sick people. (And if you get sick, please stay home.)

Is the vaccine safe?

The H1N1 vaccine is made the same way as the seasonal flu vaccine. The manufacturers just tweaked the recipe with the new virus. The Food and Drug Administration approved the vaccine in September. People with allergies to chicken eggs, however, should not be vaccinated as eggs are used to make the vaccine.

I got a seasonal flu vaccine last month. Why won’t that work against H1N1?

For the same reason that your flu vaccine from last year doesn’t protect you from this year’s seasonal flu: There are many different types of flu virus, and they mutate over time. When you are exposed to one type, your body’s immune system learns to protect you from that type only. The others are too different to register with your immune system as the same virus.

I’ve heard that in other countries the vaccine contains squalene. What is it and why is it in their vaccine and not ours? And what about thimerosal?

Squalene is a type of naturally-occurring oil found in plants and animals (including humans). Squalene is a component of some adjuvants of vaccines. Adjuvants help a vaccine’s effectiveness by boosting the immune response. Some countries have added the squalene-containing adjuvant to their vaccine mix for H1N1 because it causes a lower dose of vaccine to be effective; that is, it will allow people to get more doses out of the same batch of vaccine. The World Health Organization has found no evidence of any adverse events in vaccines containing the squalene adjuvant.

The United States government chose not to use any adjuvants in the H1N1 mix in this country. However, some formulations of the vaccine do contain thimerosal, a mercury-based preservative that has been used in vaccines for decades. Getting mercury injected into your body may sound a little scary. But concerns about safety of thimerosal are unfounded. Some parents worry that thimerosal may cause autism in young children, but there is no evidence of this. Several studies in recent years have examined the possibility, but no association has ever been found.

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