How are Covid vaccines produced and why have there been delays?

The newness of some of the technology and gaps in global preparedness have led to bottlenecks

When the first Covid-19 vaccines were approved in the UK and elsewhere three months ago, many thought the end of the pandemic was almost within reach.

Few, however, had anticipated the vast logistical problems involved in mass-producing and delivering billions of doses globally. This has been underlined by the high-profile political squabbles between the UK and EU over who should get which deliveries of vaccines from which factories amid shortages of doses.