LONDON (AP) -- To fight pneumonia, the world's top killer of children, United Nations officials say they need $39 billion (euro26.35 billion) over the next six years.

On the first World Pneumonia Day on Monday, the World Health Organization and UNICEF are releasing a global plan aiming to save more than 5 million children from dying of pneumonia by 2015.

The plea for money is less than what has been spent on more high-profile diseases like AIDS, despite the fact pneumonia kills more children than AIDS, malaria and measles combined.

"This is very simply the biggest killer people never hear about," said Orin Levine, a public health expert at Johns Hopkins Bloomberg School of Health, who has advised WHO and UNICEF. Pneumonia accounts for about 20 percent of all child deaths every year; AIDS causes about 2 percent.

Some experts say the neglect of pneumonia is the health community's own fault. "While public health experts have long known the scope and severity of the scourge, they haven't effectively mobilized the backers to put pneumonia on the map," said Mary Beth Powers, a child health expert at Save the Children.

To change that, the U.N. is promoting a variety of strategies from vaccination to generalized interventions that address economic development. Pneumonia deaths are strongly linked to malnutrition and poverty.

While officials agree pneumonia deserves a much larger share of the global health budget, not all are convinced the U.N. plan is on target.

"Trillions of dollars have been spent on promoting economic development over the last 50 years, with very little evidence such spending has made any difference," said Philip Stevens, of the International Policy Network, a London-based think tank. "Much of the U.N's nearly $40 billion will be wasted unless they stick to vaccination."

Buying vaccines to protect children from pneumonia is precisely what GAVI, a global alliance of U.N. agencies and private partners like the Bill & Melinda Gates Foundation, plans to do. GAVI hopes to raise $4 billion to vaccinate about 130 million children in 42 poor countries by 2015.

Since 2000, a vaccine to protect children from pneumonia has existed, but is only available in rich countries. "Children in poor countries have the same right to health, the same right to be immunized as children in rich nations," said Julian Lob-Levyt, GAVI's CEO in a statement.

With renewed attention and resources on pneumonia, health officials hope to slash the number of deaths in half in the next few years. "Until now, pneumonia has been off the radar," Levine said. "But this is a big problem that can be solved."

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