By Jill McGivering
The global campaign to eradicate polio has been given a grant of $200m (£97m) from the Bill and Melinda Gates Foundation and Rotary International.
The WHO says the grant comes at a critical time in the polio campaign
It comes as the World Health Organization (WHO) is calling for more donations to boost its drive to eradicate the disease altogether.
In the last 20 years, immunisation programmes have dramatically cut the number of new polio cases.
But it is still endemic in Nigeria, Pakistan, India and Afghanistan.
In the late 1980s, about 360,000 children a year were being paralysed by the disease.
Now that is down to just over 700 a year, but attempts to eradicate polio altogether have so far failed.
Earlier this year the WHO launched a fresh campaign calling for greater commitment from the developed world.
The WHO's director general, Dr Margaret Chan, said the donation is coming at a critical moment.
"The last pockets of this disease are the hardest and the most costly to reach," she told the BBC.
"This investment is also precisely the catalyst we need to mobilise additional resources. We can achieve a polio-free world if the rest of our financial partners stepped up to the challenge."
In countries where the virus is still endemic, immunisation programmes have met a range of problems.
Polio is still endemic in four countries, including Afghanistan
The communities where people are most affected tend to have poor health services. It can be difficult to reach the children and to keep track of them for repeat doses.
Parents do not always understand that the vaccine needs to be given more than once and may refuse it.
Sometimes there are cultural obstacles. If the people doing the vaccinations are young or inexperienced, for example, they might be refused.
If they are male, the women in conservative households may not let them in.
Sometimes false rumours that immunisation will harm children also puts people off.
But health workers insist that, with extra support, eradication is now within reach.