The varicella vaccine is almost 90 per cent effective against chickenpox, but its impact on herpes zoster (shingles) is unknown and needs wider surveillance, Yale School of Medicine researchers write in recent New England Journal of Medicine (NEJM) perspective section.

The varicella virus causes both chickenpox and herpes zoster, which occurs when a latent virus in the brain becomes reactivated and causes a painful rash on the skin, leading to severe pain and burning along nerves. Zoster affects people with compromised immune systems, such as the elderly. Since 1995, when the varicella vaccine was first introduced in the United States, it has greatly reduced the number of chickenpox cases and deaths from varicella. The vaccine may also have a key role in preventing zoster, the study says.

"Even though it has been shown that varicella vaccine has had a major impact on the epidemiology of chickenpox in the US, we do not know what impact, if any, the widespread use of varicella vaccine will have on the epidemiology of herpes zoster or shingles-its incidence, age distribution and severity," said Marietta Vazquez, an author on the article and assistant professor in the Department of Paediatrics at Yale School of Medicine.

Referring to a study in the same issue, Vazquez and co-author Eugene D. Shapiro, professor in the Departments of Paediatrics and Epidemiology and Public Health at Yale, note that the study shows a significant decline of 66 per cent in mortality due to varicella.

"These findings are relevant because they emphasize the importance of continuing the varicella vaccination program," Vazquez said adding, "It is possible that varicella vaccine may be useful in helping prevent zoster if it is administered to elderly persons who have had chickenpox. The long-term effects of universal vaccination on both chickenpox and zoster need to be assessed so that the vaccine policy can be modified, if necessary."