Seventy per cent of the 11 million child deaths a year in developing countries are due to five main causes - all of which are preventable.

Around three in every four children seen by health officials in developing countries are suffering from pneumonia, diarrhoea, measles, malaria and malnutrition.

Vaccines are a major plank of efforts to reduce child mortality, but they are expensive.

Carol Bellamy of Unicef says at least four million child deaths a year were "totally preventable" because of new vaccines coming on stream.

Pneumonia

The leading cause of deaths in children under five is acute respiratory infection (ARI), mostly in the form of pneumonia.

Over two million children die a year of ARI and health officials believe many other deaths attributed to different causes are in fact due to respiratory illness.

Vaccines can hugely reduce the spread of disease

However, recent trials of a vaccine against Haemophilus influenzae type b, the second most common cause of pneumonia, have shown 100% effectiveness.

The second most serious killer of children under five in developing countries is diarrhoea. Two million children a year die from it.

However, up to 90% of cases can be prevented or treated.

Diarrhoea

Diarrhoea is caused by a variety of infections, but the most virulent is rotavirus, which kills one million children a year.

There are 14 types of rotavirus, 10 of which infect humans.

The virus is passed on by children coming into contact with contaminated animal faeces or possibly by breathing in its dust.

Symptoms include fever, diarrhoea and vomiting. It can lead to severe dehydration which in turn causes lethargy and rapid breathing.

A vaccine exists which is made up of four of the most common rotaviruses.

It is thought to be between 50 and 80% effective, but work is being done to improve its success rate.

The vaccine costs around $90 per child.

Liver disease

Hepatitis B, which causes acute liver infection and cancer, can lie dormant for many years, but vaccination in childhood is 90% effective.

In sub-Saharan Africa, hepatitis B infection is thought to be carried by up to 90% of the population. It kills at least 180,000 people a year.

With prevention programmes, children can grow up healthily

Liver cancer is the leading cause of death from cancer in African men.

The economic impact is immense since liver cancer is 100% fatal in Africa and usually strikes men aged between 35 and 45.

Despite attempts by the WHO to introduce the hepatitis B vaccine to all countries by 1997, many, particularly in Africa, do not routinely vaccinate their children.

So far, only Botswana, Gambia and South Africa have a universal childhood immunisation programme for hepatitis B.

Part of the reason for this is money. Countries are dependent on donors for their vaccine supply.

Moreover, the vaccine costs more than most other childhood vaccines.

The World Health Organisation and Unicef's Integrated Management of Childhood Illness aims to tackle the multiple causes of child disease in a three-pronged approach.

This involves speeding up urgent treatment for seriously ill children, involving parents in treating children at home and prevention of disease through improved nutrition, immunisation and encouraging breastfeeding.