In war-torn parts of the world, the distant whine of a drone can signal death and destruction.

Key points: One in five Vanuatu children don't get all the vaccines they need

One in five Vanuatu children don't get all the vaccines they need Locals sometimes have to walk for days to receive medical necessities

Locals sometimes have to walk for days to receive medical necessities Australian company Swoop Aero designed a drone to deliver vaccines

But on the Pacific island of Erromango the sound means help has arrived.

We're standing in a tiny village called South River. It's perched on Erromango's west coast, in the nation of Vanuatu.

It's impossibly beautiful. Rainforest giants tower over simple, immaculate huts. A crystal clear river loops past lazily.

You hear it well before you see it. It's an angry, insistent buzz which blossoms into something like a roar.

Then suddenly the drone screams into view. It soars above you with improbable speed before stopping and beginning a slow, careful descent.

It comes to rest in a lurid green field littered with cow pats.

It's a strange and alien looking thing, a collection of right angles with small, furiously whirring blades.

But it's bearing precious cargo: vaccines for children.

Remoteness contributes to the struggle to get vaccines to all children in the Pacific nation. ( ABC: Stephen Dziedzic )

The magnitude of isolation

Vanuatu is a hard country for the workers charged with making sure every child is protected from diseases like measles, hepatitis and tuberculosis.

It has more than 80 islands sprawling over a vast stretch of the Pacific. Many are mountainous and sparsely populated.

At the moment about one in five children in Vanuatu don't get all the vaccines they need.

And it's not hard to see why. Nurses who vaccinate children often have to walk for hours or days to reach remote communities connected by nothing but muddy walking trails.

Len Tarivonda, Vanuatu's Director of Public Health, says the challenges are formidable.

"Many of the communities in Vanuatu on larger islands are quite isolated. There are small pockets of communities here and there with no access to roads, perhaps no access to telecommunications or air links," he says.

If you want to get a sense of the magnitude of this isolation, try travelling to South River.

A Swoop Aero drone comes into land at Cook's Bay, a remote village on Erromango Island. ( Supplied: Unicef/Jason Chute )

First you take a small plane from Vanuatu's capital Port Vila, landing on a runway carved out of Erromango's jungle.

Then you drive down a dirt road — one of just two on the island — to the island's largest village, William's Bay.

Finally, you get on a small motor boat for a bone-jarring two-hour ride down a rugged coastline, before turning into the sheltered inlet where South River sits.

The trip is tiring — but it's a luxury most locals here can't afford.

If they want to get anywhere they have to walk. For days.

That means they face long, exhausting treks if they want to take their children to see a nurse to get their child vaccinated.

Boys in the remote South River, in Vanuatu, where vaccines have been delivered by drones. ( ABC: Stephen Dziedzic )

Nurses do hike to South River with vaccines stored in cold boxes on their backs, but delays are inevitable.

And Cate Heinrich from UNICEF says nurses sometimes bring the wrong vaccines because communication with parents here is so difficult.

"The local nurses sometimes reach villages with the vaccines that they think are needed, but other children have come in," she says.

"The records might not be up to date because it's so hard to get into these villages."

That's where the drones come in.

The drones that deliver vaccines to hard-to-reach places in Vanuatu. ( Supplied: Swoop Aero )

Technology transforming treatment

The drone which soared into South River took about 20 minutes to cover the distance which our boat covered in two hours.

It can travel at more than 100 kilometres an hour, and costs about $4 an hour (in battery power) to run.

This marvel was built and developed by an Australian company called Swoop Aero, which is run by twenty-somethings in a rush to make a difference.

Swoop Aero co-founder Eric Peck brims with restless energy. He's a drone evangelist — and he believes their time has come.

"It's something that has been around for quite a while now, but we're at this inflection point where for the first time we are seeing the cost of the technology get down to a point where it's economically efficient to use it," he says.

"And people are getting used to drones being in the air space and being around them. So there's a social willingness to allow them to be used."

For now, this is only a trial. Swoop Aero has been contracted by Vanuatu's Government, and the program is being funded by UNICEF and the Australian Government.

What's being tested is whether this radical new solution is both practical and cost effective — and whether it can be scaled up.

The South River drone contains a small esky nestled in its body.

Before drones delivered the medicine, Sarah would have to walk for two days to get vaccines. ( ABC: Stephen Dziedzic )

Inside that are a host of vaccines, including a measles and rubella vaccine which will soon be injected into a little girl called Noeline.

When the local nurse jabs her in the thigh she barely winces, drawing a small smile of relief from her mother, Sarah.

Sarah is shy. She's unaccustomed to strangers, and agrees to talk with a touch of reluctance.

But she becomes more animated when asked if the drones have made her life easier in the few weeks since this trial began.

"Before the drones came we would have to take babies and walk to the main village to see someone [for vaccines]," she says through a translator.

She's talking about William's Bay, where our boat set off.

How long would that walk take?

"I would have to get up and walk for one day or two days to get there," she replies.

That's in one direction. So the round trip?

About four days.

And it's not just mothers who are spared the trek.

Baby Joy Nowai is the first to be vaccinated by commercial drone-delivered vaccine. ( Supplied: Unicef/Jason Chute )

The drones could potentially improve health care in villages like South River by allowing nurses to spend more time helping the sick, and less time hiking from hamlet to hamlet to offer vaccines.

It's no wonder people in Vanuatu are starting to dream about a future full of magnificent flying machines spiriting every conceivable good from village to village in record time.

This trial hasn't finished yet, and Vanuatu's Government is keen to stress they will not get swept up in enthusiasm. They will study Swoop Aero's performance carefully before they commit to expanding the program.

But Mr Tarivonda confesses that some of his colleagues in other ministries are already starting to hatch plans.

"For example in a place like this, in South River, when it comes to election time, ballot papers need to be dispatched to all communities, even in isolated areas," he says.

Crowds gather around to see the test flights of the new drone. ( Supplied: UNICEFPacific/2018/Chute )

Why not use drones?

Not long ago that might have sounded like a mad fantasy.

But after you've stood in a field on a speck of an island and watched a drone lift itself effortlessly into the sky before screaming out of sight in a heartbeat?

It just sounds like the near future.