Inside the world's biggest vaccine factory, India's Serum Institute

The tiny clinking vials supervised by silent PPE-wearing technicians belie the excitement inside the world's largest vaccine manufacturer, the Serum Institute of India, a major player in the fight against coronavirus.

Unlike the rival Pfizer-BioNTech vaccine, Covishield can be stored and transported using standard refrigeration.

Even before the pandemic, the Indian firm was a world leader in vaccines, producing 1.5 billion doses a year and inoculating two out of three children in 170 countries against diseases such as polio, mumps, meningitis and measles.