Ewan is following three of the world's toughest cold chains, supported by Unicef, who immunise over half of the world's children. In the second episode, Ewan journeys up the mighty Congo River, where he passes through frontier towns in the wilds of Central Africa, encounters a unique subculture for whom style is a religion, and ventures deep into the jungle in search of Pygmy tribes. Ewan said of his experience: 'The cold chain routes these vaccines follow can be hugely challenging and adventurous, and I was keen to explore some of them to discover how they reach the world's most remote children.

In the first episode Ewan, who has been a Unicef ambassador for eight years, follows a route that takes him through India. In a country with a booming population, often on the move, the cold chain is a race against time to stop polio before it can enter the country and spread. From India, Ewan continues his journey into the isolated wilderness of Nepal. He must endure a gruelling two-day trek to reach a tiny community secluded high in the Himalayas, but not before attempting to land at one of the world's most dangerous airstrips.