What is disease x?

One of the UK's most secretive centres of scientific research - Porton Down - is aiming to stop the next pandemic "in its tracks".

Located in the Wiltshire countryside near Salisbury, UK, the new facility is one of the few places in the world equipped to research some of the most dangerous viruses and bacteria.

The new vaccine research centre is concentrating on three main things: known infections that are getting harder to deal with, like antibiotic-resistant superbugs, potential threats like new Covid variants and "Disease X" - something unforeseen that takes the world by surprise.