'I'm very excited,' says Dr Freddie Coker, a paediatrician in Sierra Leone. 'As a doctor, I usually spend sleepless nights trying to see how much I can contribute to reducing the infant mortality rate among under-fives in my country.'

Dr Coker is responding to the promise made by a number of drug companies to reduce the prices of vaccines in developing countries - making medical help available to those who could never afford it on their own. This good news announcement has been made ahead of a London conference at which political leaders will consider how to raise funds for immunisation around the world.

The promise will have surprised many, as pharmaceutical companies have not always been good news for the poor. In 2006 they were shown to be exploiting the homeless and illiterate in India to conduct clinical trials that hadn't even been tried on animals.

But working with the Global Alliance for Vaccines and Immunisation (GAVI), big players in the drug industry such as GlaxoSmithKline (GSK), Merck, Johnson & Johnson and Sanofi-Aventis have had a change of heart.

GSK, for instance, has agreed to sell a rotavirus vaccine that prevents diarrhoeal disease in the poorest countries for £1.50 a dose - a twentieth of its £30 price in developed countries.

Why does this matter? Rotavirus-related diarrhoea kills more than 500,000 children a year on the African continent.

'About 40% of cases we see are due to diarrhoea diseases,' says Dr Coker. 'The mortality rate can be as high as 50%. The earlier a child is commenced on treatment, the better the outcome.'

Andrew Witty, Chief Executive of GSK, says drug companies need to make a profit in order to invest in developing the next generation of vaccines, so someone has to pay - but it shouldn't be those least able to.

'It's obvious that if you're in Kenya or a slum in Malawi or somewhere like that there is no capacity for those people to contribute to it - so they have to be helped out by the contribution from the middle and the richer countries.'

The business of medicine

Many people think private companies should not be in charge of producing and developing life-saving medicines like vaccines. They say that drug companies are only interested in profit and don't care about global health.

But Andrew Witty claims they do. He says drug companies are 'in step with society' and are trying to find ways of doing business that not only make a profit but also address the world's urgent health needs. Critics will dismiss this as a publicity stunt but whatever the motives, lower prices will help Dr Coker save a lot more lives.