Question:   Can I do anything to avoid the "hot lots" of vaccines that I've heard are more likely to cause reactions?

Paul Offit, M.D.:   Activist groups publish lists of the serial numbers of "bad batches" of vaccines that are associated with more reports of adverse reactions — you may have heard about them on TV news stories or the Internet — but avoiding these batches, or lots, won't protect your child. Here's why:

Just because someone has reported to the government that a child had a fever soon after getting a shot, it doesn't mean the vaccine caused the fever. He could have a cold, or the flu, or any number of things. In other words, if your child comes down with an illness a few days after receiving a vaccine, you'll naturally associate the two events, but can't know for sure if one had anything to do with the other.

More importantly, a higher number of reports about a particular lot doesn't mean it's worse than any other lot. The size of these lots varies widely. Larger lots are likely to be associated with more reports of reactions simply because more people are exposed to them. And lots that are given to babies will also seem to be causing more problems because children tend to get sick more often during their first year of life. So knowing that one lot was associated with more reactions than another wouldn't actually tell you anything about the relative safety of the two lots — even if you knew for sure that the vaccine did cause the events, which you can't.