Thimerosal, squalene and Guillain-Barré: Expert answers to your seasonal and H1N1 flu questions

Thimerosal, squalene and Guillain-Barré: Expert answers to your seasonal and H1N1 flu questions
by Children's Hospital Boston staff on October 2, 2009

In the last couple of weeks, Thrive has published several postings concerning the seasonal and H1N1 flu. Many of our readers have questions concerning the safety of these vaccines. We spoke to Children’s Hospital Boston’s Kenneth McIntosh, MD, a senior physician in the Division of Infectious Diseases. Here, he answers many of your questions, on everything from thimerosal and squalene to Guillain-Barre and how many shots is too many for a baby.

Does the H1N1 vaccine contain thimerosal?

Some doses of the H1N1 vaccine will contain thimerosal, the preservative wrongly linked to autism. When we talked earlier this week on this blog and our Facebook page about whether people should have their children vaccinated for H1N1, several readers, including several clinicians, chimed in to say that they would not get the H1N1 vaccine if it contained thimerosal. But it’s important to understand that the overwhelming scientific evidence (here and here) shows that thimerosal does not cause autism. If you want more information on this topic, the CDC has a lot of great information on their site.


I am concerned about the use of squalene in the H1N1 vaccine this year and have heard it is more dangerous (especially for our children) than getting the flu.

The vaccines that are being used in this country against H1N1 do not include any squalene, which is a molecule that is present in the human body naturally. So you do not have to worry about this. Most vaccines contain adjuvants, which are pharmacological or immunological agents that enhance the effect of the vaccine while having few if any direct effects when given by themselves. A vaccine adjuvant containing squalene (MF59) is licensed in Europe, but not in the U.S. In fact, however, most scientifically reliable reports do not support the idea that MF59 is dangerous.


There are some who believe that squalene, which was found in small amounts in some lots of anthrax vaccine, was responsible for the Gulf War Syndrome. However, there is considerable disagreement about this, and I don’t believe that a final answer is in. It is not at all clear that including small amounts in a vaccine would be harmful. In any case, the vaccines licensed in this country do not contain it.

Why did the swine flu vaccine in 1976 cause Guillain-Barré syndrome? If this vaccine is very similar to the seasonal vaccine, which is considered safe, what went wrong with the 1976 vaccine and what are they doing to prevent this again?

Good question. No one knows why the 1976 swine flu vaccine was associated with Guillain-Barre syndrome (GBS). The good news, however, is that all the influenza vaccines since that time have been tested very carefully to see whether they would cause GBS, and none have. And since 1978, vaccines have included H1N1 strains (like, but not identical to, the 1976 swine flu vaccine, and also like the 2009 H1N1 strain), and no GBS has resulted. So the chances are very good that this one will not cause GBS.


Do we really know if it’s safe to give young children three flu shots in one year (one seasonal/regular flu shot and two swine flu shots)?

Vaccines represent only a tiny, tiny fraction of the challenges faced by a child’s immune system, even that of a very young child. Babies get an average of eight respiratory infections and several intestinal infections per year, and each of these presents multiple antigens that challenge the immune system. Three flu shots really are quite safe from that point of view.

Of course, no vaccine, no medicine, is 100 percent safe, but taking your child to the playground is not absolutely safe either. Serious reactions to today’s childhood vaccines (lasting longer than a few days) are extremely rare.


I’ve heard that getting the seasonal flu shot will make you more susceptible to the swine flu because it trains your immune system to be lazy.

This is a theoretical concern that has to do with which influenza strain a person is exposed to first. It probably does not apply to vaccine-exposure at all, but here is the story. What seems to happen is that when people get influenza A (the seasonal flu) for the second, third, or umpteenth time (we all get it more than once, and many of us get it many times during our lives), our immune system seems to remember the response we had to it the first time, and even if the umpteenth strain is somewhat different from the first (although they are still enough alike that we call them both “influenza A”), we produce an immunologic response that still looks something like our first one.

In experiments with animals, this also happens with vaccines. So, getting back to your question, for adults, and even for older children, this concern doesn’t apply to the order that this year’s vaccines are given. This is because essentially all adults and older children were exposed to influenza A for the first time many years ago, and it is that first infection that produces this odd effect. For small babies, who have never had influenza, it might apply, but the best results that have shown such an effect with vaccines are in mice, and we all know that mice are NOT humans, particularly in their immune systems, and react very differently to vaccines. If you are still worried, then you can let your child get the 2009 H1N1 vaccine first and wait until after that to give your child the seasonal flu vaccine. However, I myself would not be worried.