The team, at Britain's Public Health Laboratory Service, said that although vaccination would save thousands of lives over time, thousands of elderly people could also die from the complications of herpes zoster.

Writing in the journal Vaccine, they called for a re-evaluation of the policy of mass varicella vaccination that has been introduced already in the United States and is imminent in many other countries. In 1995, the varicella vaccine was approved for use in children older than 1 year in the US and is now required for school entry.

Dr. Marc Brisson and his team report that adults living with children have more exposure to the virus and enjoy high levels of protection against shingles. Being close to children means that adults are exposed to the varicella, which acts like a "booster" vaccine against reactivation of the infection, they believe. But if all children were vaccinated, adults who have had chickenpox would not receive ongoing exposure, and would therefore be at greater risk of developing shingles.

The researchers worked out a mathematical model that predicts that eliminating chickenpox in a country the size of the United States would prevent 186 million cases of the disease and 5,000 deaths over 50 years.

However they said it could also result in 21 million more cases of shingles and 5000 deaths.

The PHLS said in a statement it was working out what the impact might be of introducing a chickenpox vaccine in Britain.

"As more evidence becomes available, it will be shared with the Joint Committee on Vaccination and Immunisation (JCVI) which advises the Department of Health on the immunisation schedule."