What is a cold chain?
A high-quality cold chain allows health workers to deliver life-saving vaccines to every last child.
Each year, UNICEF delivers nearly three billion vaccine doses, enough to immunize almost half of the world’s children.
Delivering vaccines to all corners of the world is a complex undertaking. It takes a chain of precisely coordinated events in temperature-controlled environments to store, manage and transport these life-saving products. This is called a cold chain.
Vaccines must be continuously stored in a limited temperature range – from the time they are manufactured until the moment of vaccination. This is because temperatures that are too high or too low can cause the vaccine to lose its potency (its ability to protect against disease). Once a vaccine loses its potency, it cannot be regained or restored.
How do vaccines move along the cold chain?
In July 2025, UNICEF delivered its first-ever vaccine shipment by sea. Carrying over 500,000 doses of pneumococcal 13-valent conjugate vaccines, the refrigerated cargo ship travelled from Belgium and safely arrived in Abidjan, Côte d’Ivoire, paving the way for expanded use of sea transport in future vaccine deliveries.
UNICEF mainly uses air transport to deliver vaccines quickly, with a few shipments travelling by road. All vaccines are shipped as refrigerated cargo directly from the manufacturer to the country, where they will be used. To make vaccine deliveries more sustainable and cost-effective, UNICEF is also exploring sea shipping, which could reduce greenhouse gas emission by up to 90 per cent and freight costs by 50 per cent per shipment compared to air transport.
Once the vaccines arrive in the destination country, they are stored in cold rooms before being distributed to regional and sub-regional cold storage facilities by refrigerated vehicles.
From storage facilities down to the village level, health workers carry vaccines in cold boxes and vaccine carriers, travelling by car, motorcycle, bicycle, donkey, camel or on foot to immunize every last child, even in the most remote of villages.
Keeping vaccines safe and effective
Storage and transport equipment such as cold rooms, refrigerators, freezers, cold boxes and vaccine carriers must comply with performance standards defined by the World Health Organization (WHO). Stock management procedures must also follow WHO guidelines specific to each type of vaccine.
UNICEF procures cold chain equipment and services, and works closely with partners and governments to ensure that the cold chain is unbroken and that systems continue to work efficiently in every country, keeping vaccines for children safe and effective.
