Dear Dr. K: I had shingles three years ago and now I have it again. I thought you were only supposed to get shingles once.

Your impression and what I was taught in medical school are identical, but, unfortunately, are now incorrect. There are probably two reasons for this change. One reason is that until a disease state is subjected to critical analysis, misjudgments of incidence and frequency can be made. The other is that due to modern antiviral drugs the disease itself has changed. In other words, before we had antiviral drugs to treat the shingles, the illness could be quite severe causing nerve damage, scarring of the skin and, in some cases, blindness.

But because of its severity it elicited a strong immune response and therefore a strong resistance to further outbreaks.

The use of the new antiviral drugs is very helpful in treating the shingles and preventing complications, but their result can be a less permanent immune resistance.

The Mayo Clinic has researched these trends and in its patient population they find 6.2 percent of people have a second attack of shingles within eight years. The rate was highest in people who had severe pain with their first episode. It was also higher in women and persons past the age of 50.

One new weapon in the war on shingles is the new vaccine Zostavax. It currently is recommended for adults 60 years and older as a one-time shot to help prevent shingles.