Diarrhoea caused by the intestinal infection rotavirus kills 1m children every year in developing countries, and puts millions of others into hospital.

The new vaccine, RotaShield, could save thousands of lives by combating the infection.

The drug is designed to be taken by children three times during the first year of life, at two months, four months, and six months.

The US Food and Drug Administration has warned that cost may prevent the vaccine's widespread use in developing countries.

Developing countries targeted

But manufacturer Wyeth-Ayerst Laboratories has pledged to get the vaccine to children in developing countries, probably by using profits from rich countries to subsidise poor ones.

Dr Albert Kapikian, who has worked on a vaccine for 24 years, said: "It's very exciting news. I think it's going to have a major impact."

Rotavirus is the leading cause of severe childhood diarrhoea, attacking the lining of the small intestine.

In severe cases, a child can experience 10 to 20 episodes of diarrhoea in a single day, quickly getting dangerously dehydrated.

Infects most children

Vaccine proved effective in Venezuelan study

Dr Kapikian said rotavirus infected approximately 75% of all children before the age of five years.

One in 40 children is hospitalised, but good health care, especially replacing lost fluids, limits deaths.

In studies of US infants, RotaShield prevented between 70% and 90% of severe diarrhoea, although it did not eliminate rotavirus.

A study in Venezuela last year concluded the vaccine was equally effective in developing countries.

Professor John Calam, of the gastroenterology department at Hammersmith Hospital, London, said: "This sounds like a big breakthrough. However, it may be that the people who really need it - the six month old children in Bangladesh - cannot get it."

Side effects

The main side effects of the vaccine are low fevers, irritability and decreased appetite within five days of the first doses.

The FDA said it is safe to give RotaShield, an oral vaccine, at the same time as vaccines against polio, diphtheria, whooping cough, tetanus and a form of meningitis that infants also get by six months of age.