The vaccine might have spared 13-month-old Eustin from meningitis

It is the first proof a vaccine could have such a big impact on death rates in Africa, say the authors - similar to the effect of bed nets on malaria.

Vaccinating 17,000 infants against a bacterium that causes deadly pneumonia and meningitis cut mortality by 16%.

Streptococcus pneumoniae kills up to one million children under five worldwide each year.

Most of these occur in the developing world.

This is the first time we have really had proof that the vaccine prevents pneumonia deaths Researcher Professor Brian Greenwood

Vaccines against pneumococcal disease have been available for about four years.

While studies in America and South Africa have shown such vaccines work, none has looked at whether they stop people dying.

In the four-year study in The Gambia, supported by a broad coalition of international partners including the World Health Organization and the UK Medical Research Council, the pneumococcal vaccine not only reduced deaths, but hospitalisations and cases of pneumonia.

The children who received the vaccine had 15% fewer hospitalisations and 37% fewer cases of pneumonia than the children who did not.

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Dr Felicity Cutts, principal investigator of the trial who is currently based at WHO, said: "Pneumococcal pneumonia, meningitis, and sepsis are major causes of death and serious illness among African infants and young children.

"The trial results are highly promising.

"Vaccination can prevent many of these serious infections even in a rural African setting. This is great news for children and parents in rural areas everywhere."

Co-research Professor Brian Greenwood, of the London School of Hygiene and Tropical Medicine, said: "This is the first time we have really had proof that the vaccine prevents pneumonia deaths.

"There have been very few interventions that have had this effect on deaths since bed nets for malaria."

Dr Lee Jong-wook, director-general of WHO, said the task now was to make the pneumococcal conjugate vaccine widely available to children in Africa.

"Immunizing children with pneumococcal conjugate vaccine in developing countries will be a critical intervention towards achieving a two-thirds reduction in the under-five mortality rate, a Millennium Development Goal," he added.

A spokeswoman from UNICEF said: "In The Gambia, routine immunization is high, and the outcome of this study will compliment further the efforts of UNICEF in its role in child survival."

Professor Greenwood said provision across Africa was patchy, with some countries having good access to vaccines and others having poor access.