Chickenpox, one of the most common infections of childhood, is killing a growing number of adults, scientists warn in research published today.

A steady rise in fatalities over the past 30 years means the virus is likely to claim the lives of at least 25 adults in England and Wales each year.

More than 80 per cent of those now killed by chickenpox are adults, who contract a much more severe form of the disease than children. Deaths are twice as common in men as women, and males aged 15 to 44 are most at risk, the study published in the British Medical Journal concludes.

Professor Norman Noah, from the London School of Hygiene and Tropical Medicine, who led the research, said: "Chickenpox is not a mild disease. This study confirms that chickenpox causes considerable mortality in adults and may be increasing in importance. Deaths in adults have increased both in number and proportion. Our figure of 25 deaths a year is probably an underestimate."

The study shows that adults accounted for 48 per cent of all deaths from chickenpox in the early 1970s. That figure increased to 64 per cent in the early 1980s and has now reached 81 per cent.

Professor Noah said his study could not explain why more adults were dying. But he warned: "If adults get chickenpox they should realise it is different from the childhood disease. They are at greater risk and need to see a doctor much earlier."