Measles is a highly contagious, horrific disease. If left untreated it can lead to death. There's no specific treatment. All us medics can do is isolate the sufferer, give them vitamin A, and hope for the best.
In high-income countries like the UK most people infected with the disease recover in a couple of weeks. Very few die. But in developing countries it kills up to one in five. As we mark World Immunisation Week (April 24-30), we must ensure children everywhere have access to vaccinations that families in the UK take for granted.
A safe and cost-effective vaccine to protect children from measles does exist. But families in remote areas, in countries with weak health systems, struggle to access it and other essential vaccinations that can protect them from preventable diseases.
An emergency unfolds
Mayom County, in rural northern South Sudan, is one such place. A remote population in a country crippled by civil war, no children have received routine vaccinations here for over two years. In early 2016 a few suspected cases of measles appeared, dotted around the main town. In less than two months, the county was in the grip of a full-blown outbreak.
Nearly three quarters of the cases were children. Tens of thousands of children were at risk.
Previously in situations like this, we would have to spend time pulling together teams of specialists and supplies - a delay that costs lives. But now Save the Children has revolutionised the way we get medical care to children in emergencies.
Our Emergency Health Unit is made up of fully-formed teams of medics and specialists on standby all over the world, ready to deploy within hours - complete with equipment, supplies, and logistics specialists like myself, with the skills to get everything where it's needed quickly.
While 86% of children around the world now receive the most basic vaccinations, protecting them from such diseases as pneumonia, measles and hepatitis B, many are still left behind.
19.4 million children under the age of one are still missing out. That's 1 in 7 children around the world missing out on life-saving immunisations. We've been fighting to achieve universal immunisation coverage for children, working around the world to try and give all children a healthy start in life.
Children from the poorest households, certain ethnic groups, living in neglected areas, and affected by conflict and emergencies are more likely to be excluded from access to immunisations. Two-thirds of children living in a country affected by conflict are not immunised.
A medal of honour
As soon as we heard about the measles outbreak in South Sudan, my team was mobilised. Within two weeks of the outbreak being announced, we were on the ground vaccinating children in 18 clinics and 24 mobile outreach centres.
The infrastructure in Mayom is poor - it's difficult to reach this part of South Sudan, and many NGOs are reluctant to attempt healthcare here. We used any means possible to reach the most remote communities, including motorbikes and canoes. We travelled across rough, rugged terrain and collapsed bridges, and vaccinated children in the middle of sandstorms.
We hurried, carrying life-saving vaccines in Mayom's 40-degree heat in precious cool-boxes. All while wearing what one of my colleagues described as the 'Mayom suit': covered head-to-toe in dust.
In one rural cattle ranch our team leader, Koki, was spat on by an elderly man on our arrival. "Hey, what's this?" Koki said, wiping the slime from his forehead. It turned out this was a sign of appreciation from the old man, who in his lifetime had never seen any NGO reach his remote community. ''Being spat on by an old man signifies immense blessings bestowed upon Save the Children!'' a local health official told us.
And this salivary medal of honour felt truly earned. In this most inhospitable of environments, we did whatever it took to protect the vulnerable children in this isolated part of the world. In just three weeks, 44,447 children were permanently saved from a potentially deadly fate. A catastrophe was averted.
British aid saves lives
Immunisation saves lives. Fact. It's one of the most cost-effective ways we have of preventing illness, with an economic return of around £44 for every £1 invested. Over the past 25 years, British aid has transformed the lives of children in the world's poorest countries. Throughout that time, we've shown the world our nation's commitment, compassion and generosity. This year, six million fewer children will die needlessly than in 1990.
Immunisation is one of the most successful and cost-effective health interventions. Britain's investment in immunising children globally through UK aid in the past five years has meant that 67.1 million children - more than the entire population of Britain - have been protected against preventable diseases. The impact of this work is undeniable: UK aid saves lives. It helps the world's poorest stand on their own two feet.