JUDY WOODRUFF:

This is peak season in the United States for Lyme disease, as people spend more time outdoors and can be at risk for tick bites.

Each year, at least 30,000 cases are reported, and researchers believe those estimates are low. Given its debilitating effects on some people, and after years of research, it begs the question: Why is there still no vaccine people can get to prevent Lyme disease?

Miles O'Brien has been exploring that for his weekly reports on the Leading Edge of science and technology.