Smallpox killed countless millions – 300 million people in the 20th century alone – before it was finally declared eradicated on May 8 1980. It was a momentous day, marking what the current director general of the World Health Organization, Dr Tedros Adhanom Ghebreyesus, called the greatest “public health triumph in world history”.

British cancer doctor Prof Karol Sikora recently claimed that the current COVID-19 pandemic would “burn itself out”. His thinking is that if there are more infections than we realise, and that those milder, unrecorded infections result in robust immunity, then this would quickly lead to “herd immunity”, leaving the virus nowhere to go but extinct. Extend this to the world’s population and the virus eradicates itself.

Some people question why the current coronavirus has brought the world to standstill while a previous deadly coronavirus, SARS, did not. Others have questioned why a vaccine is so urgently needed now to stop the spread of the current coronavirus when a vaccine was never developed for SARS.