Kiwi researchers have helped narrow down the urgent hunt for a vaccine that could help save the lives of hundreds of thousands of young children and babies around the world.

A landmark international study into pneumonia, published today in major journal The Lancet, pin-pointed the deadliest forms of viruses and bacteria, revealing one vaccine that could make a big difference.

Globally, pneumonia causes more deaths among children under 5 years old than malaria, tuberculosis, HIV, Zika virus, and Ebola virus combined – about 900,000 fatalities, with more than 100 million reported cases each year.

The Pneumonia Etiology Research for Child Health (PERCH) study involved seven countries and nearly 10,000 children, and singled out viruses as the new leading cause of global childhood pneumonia.

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The findings will help shape how clinicians prevent, diagnose and treat the illness in the 21st century, and bring a new urgency to the search for a vaccine for the virus that accounted for almost a third of all cases.

"We believe they will help accelerate progress preventing deaths from pneumonia, and so contribute to children surviving and thriving globally," said Associate Professor Stephen Howie of the University of Auckland, a paediatrician who was one the Kiwi researchers behind the study.

"We have much higher rates of pneumonia than we should. Poverty, overcrowding, smoking, poor nutrition, low immunisation rates, and problems getting the treatment kids need are key factors in these high rates."

Latest figures showed New Zealand's rates of childhood pneumonia were two to five times higher than Australia, England and the UK.

Ten per cent of under-2-year-olds are hospitalised for respiratory infections in New Zealand, and our rates of pneumonia, and of death from pneumonia, are highest among our Māori and Pacific children, and children in poverty.

A total of 122 children died of the illness in the 10 years to 2015.

"Those deaths can be avoided by two things - preventing pneumonia happening, and treating it properly when it does happen."

PERCH was led by the International Vaccine Access Center in the renowned Baltimore-based Johns Hopkins Bloomberg School of Public Health, and involved more than a dozen institutions and programmes.

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It is the largest and most comprehensive study of its kind since the 1980s.

"Before PERCH we were reliant on old data from the 1980s," explained Professor David Murdoch, a renowned University of Otago infectious disease expert who led establishment of laboratories in seven countries involved in the study.

"The landscape has changed since then with the roll out of vaccines against some important causes of pneumonia, the AIDS epidemic, increased urbanisation, the development of antibiotic resistance, and availability of better diagnostic tests."

By understanding the range of viruses and bacteria causing the disease in each country, the research gave individual nations, and global agencies such as the World Health Organization, a clear battle plan to combat pneumonia.

PERCH also developed a new, high-powered statistical tool to better understand the causes of infection in children.

The hope was that tools could help doctors more accurately identify what has caused pneumonia for an individual child, enabling better and smarter treatment of children with severe pneumonia, and reduce unnecessary antibiotic use leading to antibiotic resistance.

"There used to be a strong divide between developed countries and low-and middle-income countries: bacterial causes predominated in low and middle-income countries, while viral causes were more common in developed countries," Howie said.

"The PERCH study revealed a shift to viral causes dominating worldwide."

This was due in part to successful roll-outs of vaccines against H. influenzae type b and S. pneumoniae, two important bacterial causes of pneumonia.

In the study, children who had been hospitalised with severe pneumonia were tested for viruses, bacteria and fungi.

Results showed that two-thirds (61 per cent) of all cases were caused by viruses, and a particular virus – known as the Respiratory Syncytial Virus (RSV) - accounted for nearly one third (31 per cent).

Other top causes were rhinovirus, human metapneumovirus, parainfluenza viruses, and the bacteria Streptococcus pneumoniae, Haemophilus influenzae, tuberculosis, and Staphylococcus aureus. Among the severest cases in the study, bacterial causes remained very important.

A major focus from now would be the development of effective vaccines and treatments against the important causes of childhood pneumonia identified by the study.

"Immunisation is a vital protection against infections, including many bacteria and viruses that cause pneumonia, and we need to make sure children get the full benefit of existing vaccines, as well as developing new ones, such as an RSV vaccine," Howie said.