IN 1439 King Henry VI of England banned kissing as a greeting to stop the spread of the Black Plague. Today, as covid-19 spreads around the world, authorities are encouraging similar measures to fight infection. In China, to avoid hand-shaking, people are being told to greet one another with a gong shou gesture, where a palm is folded over the opposite fist. In the Gulf, citizens are saying hello with a wave rather than the traditional “nose to nose” greeting. And in Italy and France, friends and acquaintances are eschewing the customary peck on both cheeks.

Such efforts are more effective than they might seem. A paper published in 2014 explored how greeting rituals spread infectious diseases. David Whitworth and Sara Mela, two biologists at Aberystwyth University in Wales, dipped a glove in bacteria, before using it to greet another person wearing a sterile glove. Bacteria can be transmitted in a similar way to the new coronavirus. They found that a handshake transfers almost twice as much bacteria as a high five, which in turn transmits twice that of a fist bump. The duration of greetings matters, too. Stronger and longer handshakes transfer more bacteria than weaker, shorter ones. The same goes for high fives.

Many therefore seek to avoid any contact at all. Mike Pence, the American vice-president, has taken to greeting people with the “elbow-bump”, which was adopted in some places during past epidemics, eg, of avian flu and Ebola. The “Wuhan shuffle” involves bumping feet. And in Iran, which has the worst outbreak of covid-19 outside China, some have taken to bumping hips.

Substituting handshakes for fist, elbow and foot bumps may help slow the spread of covid-19. But epidemiologists say the most reliable way to stop the fast-spreading illness, which by March 6th infected more than 100,000 people and killed 3,400, is frequent and thorough hand-washing (the WHO recommends doing so five times a day). Like the common cold, covid-19 is thought to spread via droplets of moisture ejected when an infected person coughs or sneezes, or just speaks. Even without shaking hands, people can contract the disease by touching something an infected person has come into contact with, and then touching their mouth, nose or eyes. Handwashing helps prevent this.

For many, especially in poor countries, following this advice is easier said than done. According to the World Bank, only a quarter of people in sub-Saharan Africa have access to basic handwashing facilities including soap and water. In Ethiopia, the figure is just 8%; in the Democratic Republic of Congo, 4%. Still, changing habits can help. The disease has already reached the region. On March 5th Cyril Ramaphosa, South Africa’s president, warned of a coming crisis after the country confirmed its first case. The news, as well as many meetings around the world, will be greeted with trepidation.