Scott Marmion (Letters, April 14) quotes physics genius Richard Feynman without context. Feynman didn’t say experts were ignorant, rather that there remained much for experts to discover.

Cholera is a bacterial infection which killed 38 million in six long 19th-century pandemics. The third pandemic reached London by 1852 when Dr John Snow (born North Street, York, in 1813), concluded that cholera was waterborne. A water pump in Broad Street, London, was contaminated with sewage making many ill. Snow used new methodology for analysing the outbreak. Today he is recognised as the father of modern epidemiology. Epidemiology will help decide when to lift lockdown. Snow was indeed an expert.

Transplant pioneer Sir Peter Medawar (another expert) described viruses as ‘bad news wrapped up in a protein’. Smallpox virus killed 200 million in the 20th century but was eradicated in 1977. HIV/Aids is much harder to conquer. Virus Covid-19 has now killed 12,107 in the UK; 125,196 worldwide. Let us wish the experts good luck in their search for a vaccine and a cure.

Scott Marmion says his defence against Covid-19 is ‘his immune system and his common sense’ rather than the help of experts. Really? Who will inform his common sense? Modern-day experts, of course, in the mold of York’s own Dr John Snow.

Quentin Macdonald

Church Lane,

Nether Poppleton, York