The United States State Department is denying entry to foreign nationals who have recently been to China, is screening American citizens who arrive home from China as well as asking them to self-quarantine for 14 days. It has told American citizens not to visit the country at all. Major airlines including British Airways, Lufthansa and all three major American carriers have halted all flights to China, while the cruise line Royal Caribbean is denying boarding to any person who has traveled to, from or through China or Hong Kong in the past 15 days. Travel companies such as those airlines are motivated both by pressure from employees and by the falling demand for flights. Flying empty planes to and from China is, after all, not profitable.

But what has motivated the response from governments? It doesn’t appear to be evidence. Measures like screening at airports, quarantining cruise ships or flights with confirmed cases and isolating communities at the center of an outbreak can be effective, said Erin Sorrell, an assistant research professor at Georgetown University who studies emerging infectious diseases. However, she and other experts say the available evidence suggests that total border shutdowns are not an effective means of containment of respiratory viruses. Resources are better used, she argued, treating sick patients and developing vaccines and other countermeasures.

Sadly, one doesn’t have to look far for evidence of these top-down decisions morphing into outright racism within the general population, a trend that has a long history in the narrative of outbreaks such as this one.

Coronavirus shares something in common with other kinds of civil disruption, natural disasters or emergencies that affect localized travel industries: Its destructive power lies not in the actual risk but in the perception of that risk. Numerous experts have said that the majority of people who contract coronavirus will experience it as a respiratory infection they will fully recover from. But the extreme reactions — the canceling of flights, closing of borders and level-four travel warnings — seem more appropriate for something much worse.

Therein lies a familiar unfairness. When it comes to travel, the perception of risk is rarely meted out objectively. Consider the level-two travel warning imposed by the State Department last month in the wake of the continuing Australian wildfires. It advised travelers to consider postponing their trips because of extremely poor air quality and the threat of evacuation in the monthslong fires. Just a few days later, it was reduced to level one, reportedly in response to the direct appeal of Prime Minister Scott Morrison to the Trump administration. Similarly, in the 2017-18 flu season, when the United States had a particularly bad outbreak, the respiratory virus resulted in an estimated 61,000 deaths and 45 million symptomatic cases — but no travel warnings.