World governments can save four million more lives by 2015 by vaccinating more, according to a report from the charity Save the Children.
The 'A Vaccine For All' report claims that GAVI (Global Alliance for Vaccines and Immunisations) is facing a £2.3bn shortfall in its efforts to immunise 243 million children by 2015.
A conference hosted by GAVI, held in London on Monday, will encourage governments and donors to make further financial commitments.
Needs vary from country to country. In Kenya, pneumonia causes 15% of all deaths in children under five. In India, more than 80,000 children die of measles each year.
Sky News travelled with a team from Save the Children to rural South Sudan.
In Northern Sudan , 72% of children receive a full immunisation program.
However, in Southern Sudan just 17% of children are vaccinated.
When South Sudan becomes an independent country in its own right on July 9th, it will have the poorest vaccine record in the world.
South Sudan has only 50 kilometres of paved roads and they are all in the capital, Juba.
The dirt roads to isolated, rural villages are bumpy and slow at the best of times.
During the rainy season they are impassable and the vaccines do not and cannot, get through.
Factor into that the added danger of ambush and the unpredictable tribal battles, and you can see that moving vaccines around South Sudan is far from a straightforward process.
The vaccine teams arrive in tribal villages, often on foot, and not knowing what to expect.
More often than not, young children greet them, carrying their even younger siblings.
During the day mothers harvest crops and fathers tend livestock - work is considered more important than medicine.
One woman whose baby died last month said that she first tried traditional village medicine but she took her son to the clinic when he didn't get better. Unfortunately it was too late.
"I'm not convinced western medicine would have helped," she said. "I put my trust in God. If God wants you to die you'll die. I'm now worried the grief will kill me."
Natalong lost two of her children to measles. She said: "The measles drug has come now.
"It will stop killing children like it did when it killed mine. We didn't know then we had to take our children for vaccinations. Now vaccines are available there is no delay and no one will die."
Changing attitudes and providing health education is half the battle. Western medicine is viewed with suspicion.
Needles look scary and the fact that children might feel a little ill for a day or two after being vaccinated is often considered proof that it doesn't work.
To provide that education Save the Children claims 3.5 million extra health workers are needed.
It hopes the London conference will go some way to achieving that.