One of the tragedies of these post-truth times is that the lies, conspiracy theories and illusions spread by social media and populist politicians can be downright dangerous. The denial of human responsibility for climate change is one obvious example; another is opposition to vaccination. A serious outbreak of measles in Italy and in some other European countries could well be the result of a drop-off in vaccinations caused by utterly misguided and discredited claims about their dangers.

Vaccines are among the greatest achievements of medical science, an easily and safely administered defense against once common and often deadly diseases like measles, polio, smallpox, whooping cough and cervical cancer. Yet fear of vaccines has spread over the past two decades, fueled in part by an infamous study published in the medical journal Lancet in 1998 and later retracted and completely discredited.

More recently, President Trump has added his voice to vaccine skepticism, like this utterly unfounded and irresponsible tweet: “Healthy young child goes to doctor, gets pumped with massive shot of many vaccines, doesn’t feel good and changes - AUTISM. Many such cases!” In Italy, the populist Five Star Movement (M5S) led by the comedian Beppe Grillo has campaigned actively on an anti-vaccination platform, likewise repeating the false ties between vaccinations and autism.