Oliver Conway

Deep in the Himalayas, I'm walking with 41-year-old Kamla Devi, who is a health worker on a vital mission.

Trekking along this route is quite dangerous.

The monsoon rains have washed away the roads and I'm walking between muddy and slippery stones.

This is what Kamla does every month, travelling on foot to meet children in remote mountain villages and vaccinate them against diseases like measles and chicken pox.

It's a question of a child's life.

If we miss even one dose, they won't have the protection to fight these diseases.

There can be no excuses.

Whether it rains or the roads are closed, we have to go.

She carries a cold box that must stay at the right temperature to keep the shots effective.

I have ice packs in this box to keep vaccines between 2 to 8 degrees Celsius till it's given to the child.

I've just been told there's half an hour more of this steep climb in the rocky terrain.

I'm out of stamina, but we'll make it.

As Kamala goes to these lengths to vaccinate children, across the world, childhood vaccines are facing a growing debate after US President Donald Trump questioned their safety and effectiveness.

The World Health Organization has warned that misinformation on children vaccines could undo years of progress, especially in countries like India.

Professor Rakesh Agarwal is the chair of Southeast Asia Immunization Group with the World Health Organization.

And that's why India has poured millions of dollars into training and deploying health workers like Kamala to reach the last mile and deliver free vaccines to newborn kids.

After an hour of journey, we finally reached the village of Swar.

The health centre is a yellow-coloured hut with a tin roof.

Families have gathered outside waiting for Kamala.

Among them is Preeti Devi.