Millions of children are vaccinated against disease each year

Children in developing countries are more likely to suffer side-effects from vaccines compared to those in the West.

They are also more likely to suffer pain and cry when they get immunised.

That's according to Heidi Larson of the UN children's agency Unicef. She blames a global divide on vaccines for the differences.

While richer countries are able to afford the latest vaccines, governments in the developing world sometimes rely on cheaper and older alternatives.

Less reactivity

The vaccines are equally effective but their impact on children can be different.

"The potency of the vaccines is not an issue. But in the West some of the vaccines have a little less reactivity. You get a little less redness. You get a little less crying," says Ms Larson.

The global divide also means that some children do not have access to the vaccines they need.

"When we had just the basic six vaccines, we had a lot of them and they went everywhere in the world. The old supply-demand of market forces meant the prices were low enough so that they could be affordable," says Ms Larson.

"That is changing now because the developing world is getting different vaccines. You don't get the income from the industrial world to support the lower costs. Supply is an issue."

Unicef is working with governments in the developing world to try to get accurate figures on how much vaccine they need.

This helps them to order vaccines in bulk or even encourage manufacturers to produce them again.

"We are trying to get more specific in terms of forecasting vaccine needs," says Ms Larson.

"We are really having to look much harder and work much closer on the production of vaccines and work much closer with governments and ministries of health to predict how many vaccines will be needed and getting resources and funding in particular in advance so that we can get guarantees of vaccine production."

The policy is paying off. Last year, Unicef procured 2.2 billion doses of vaccines to administer to children in the developing world.

"I think everyone would agree that it is best to prevent illness rather than waiting to cure it," says Ms Larson.

This story is featured in the radio programme Health Matters on the BBC World Service.