Wow, where did you hear that?

In 40 years of medical practice here at Harvard Medical School, where many of my colleagues are leaders in research on Alzheimer's disease, I've never heard that. Just to be sure, I searched all research articles published in all medical and biological science journals over the past decade, and could not find a single study that made such a claim. I also looked at all of the major textbooks of medicine, and none of them made such a claim, either. In other words, it's just not true.

It's also dangerous. Influenza kills 20,000 to 40,000 people each year, and flu shots protect against the disease. If people get scared about getting flu shots -- for no good reason -- they are putting themselves at risk.

Finally, based on what we know about Alzheimer's disease, it makes no sense that flu shots would be connected to Alzheimer's disease. Twenty years ago, scientists had little idea what caused Alzheimer's disease. In the past 20 years, however, we have learned a lot about the causes of the disease. We've identified a handful of molecules that clearly are important in causing the disease. None of those molecules has anything to do with the influenza virus or vaccines against the virus.

And since flu season is approaching, let's talk about another flu shot myth: that it gives you the flu instead of preventing it. The flu shot is a vaccine made of killed virus. If a virus is dead, it can't reproduce itself. And if it can't reproduce itself, it can't cause the flu.

So I hope you and other readers are reassured. There are so many things that really are worth worrying about. Let's not worry about things that are actually good for us.