Earlier this month, British artist David Hockney raised eyebrows with the suggestion that smoking cigarettes might boost people’s immunity to Covid-19. “I used to joke that being a smoker in Malibu was the equivalent of being a non-smoker in Pasadena. They used to have very bad pollution there,” he wrote in a letter to the Daily Mail. “Could it not be that smokers have developed an immune system to this virus?”