On Thursday, World Health Organization Director General Tedros Adhanom Ghebreyesus declined to declare the new coronavirus outbreak a PHEIC — a public health emergency of international concern. The pneumonia-like virus, which originated in the Chinese city of Wuhan before spreading to several other countries, prompted Chinese authorities to lock down several cities and prevent some 25 million people from leaving. These actions raise questions about the true severity of the outbreak, increasing uncertainty in an already uncertain situation.

While the WHO’s director general has the authority to declare a PHEIC, he is advised by an expert committee that was split on whether the criteria had been met. A PHEIC is (1) an extraordinary event that, (2) poses a public health risk to other countries and (3) requires a rapid international response. “This is an emergency in China,” Tedros said. “But it has not yet become a global health emergency. It may yet become one.”

When the WHO declares a PHEIC, it provides recommendations on what governments should and should not do to contain the disease while avoiding panic and overreaction. Under the International Health Regulations (revised in 2005 after the SARS outbreak), countries agreed to follow this guidance.

In the five PHEIC declarations so far, the WHO recommended against border measures such as visa or import bans, border closures, flight cancellations and even passenger screening. Although Tedros has not declared this outbreak a PHEIC, he still advised against restrictions. Already this week, several countries, including the United States, began screening travelers arriving from Wuhan. North Korea was the first to close its borders to foreign tourists.

Travel and trade restrictions might seem like a common-sense public health response — so why does the WHO frequently recommend against them? Here’s why border measures do not work, why countries often disregard the WHO’s guidance and what this might have to do with Thursday’s decision not to declare a PHEIC.

What’s the problem with trade and travel restrictions?

During disease outbreaks, the public often supports border measures. But there’s little evidence that these measures limit the spread of diseases.

Entry screening, for instance, can be ineffective because of asymptomatic carriers or long incubation periods — people can be infectious without showing any signs of sickness. And symptoms can be consistent with a range of viruses (the flu and coronavirus have similar symptoms, for example). Screening also diverts resources from proven response measures. More restrictive measures, like visa bans and border closures, may encourage travelers to find underground ways of crossing borders and discourage passenger honesty about symptoms and travel history.

Past trade restrictions also proved ineffective. During the H1N1 pandemic in 2009 (also called “swine flu”), the WHO and the World Trade Organization stressed that the virus could not be spread through pork products. Still, over 40 countries banned pork imports from H1N1-affected countries.

While these types of travel and trade restrictions don’t limit the spread of diseases, they do contribute to the substantial economic losses suffered by countries facing an outbreak, and they introduce other unintended consequences. My research shows that fear of restrictions may encourage economically and politically vulnerable countries to conceal outbreaks. Delayed or inaccurate reporting is a persistent challenge to outbreak prevention and response. Disregarding the WHO’s recommendations disincentivizes transparency and increases global vulnerability. Indeed, despite a laudable initial response, analysts see China’s shutdown of major cities as evidence that President Xi Jinping and the Communist Party, facing political and economic pressure, may have concealed the severity of the outbreak.

Despite the limited utility and potential harm of border measures, countries often ignore the WHO’s guidance. For example, during the H1N1 (2009) and Ebola (2014) outbreaks, nearly 25 percent of countries imposed travel or trade restrictions when the WHO said not to.

So why do countries ignore the WHO’s guidance?

My research points to two reasons governments don’t always follow the WHO’s guidance: They face domestic political incentives to impose border measures and anticipate few costs for doing so from the WHO and the international community.

In examining the H1N1 outbreak, I find that the countries most likely to impose trade and travel barriers were those most concerned about a negative public reaction. They used these barriers as domestic political cover in case the outbreak crossed the border and caused harm. Soon after the H1N1 PHEIC declaration, for example, Jordan imposed a ban even though imports of U.S. pork products were negligible, casting doubt that this action was in the name of public health. Jordan’s assistant secretary general for animal welfare explained that the ban was meant to allay public pressure and fear. While many governments follow the WHO’s guidance, domestic political incentives weigh more heavily for some than commitments to the IHR.

This may be particularly true because ignoring the WHO’s guidance has resulted in few consequences. During the H1N1 pandemic, 47 countries targeted the United States, Mexico, Canada and other H1N1-affected countries with pork import bans. The United States issued diplomatic warnings but did not retaliate.

For its part, the WHO relies on its members for funding and support. Given that it is strapped for cash, criticizing member countries is not always an attractive option.

As a result, as my research on the 2014 Ebola outbreak suggests, a PHEIC declaration can make matters worse by unintentionally provoking border measures. A PHEIC declaration is meant to motivate a coordinated international response. However, such a declaration also signals a serious outbreak that people and governments should worry about. In the absence of higher costs for disregarding the WHO’s recommendations, governments can feel tempted to impose restrictions. In fact, concerns about restrictions have factored into past PHEIC deliberations. Similar worries may have contributed to the WHO’s Thursday decision about the coronavirus.

Will global health cooperation improve?

There is reason for some (guarded) optimism. The WHO does recognize these dynamics. Tedros used strong language last year when WHO declared the Congo Ebola outbreak a PHEIC, stressing that border restrictions “can actually hamper the fight” and were “punitive” and “counterproductive.” He has also been willing to criticize governments, and the WHO has developed a tool to monitor compliance with its recommendations. Furthermore, countries don’t always impose trade or travel restrictions — the 2016 Zika outbreak and the ongoing Ebola outbreak provide examples that similar cooperation is possible during the current coronavirus outbreak.

There are still unanswered questions, such as the mode and ease of transmission and the number of coronavirus cases so far. But whether countries follow the WHO’s recommendations against trade and travel restrictions, especially if a PHEIC is declared, will be a sign of how well equipped the world is to deal with global health threats now and in the future.

Catherine Z. Worsnop is an assistant professor at the University of Maryland School of Public Policy, where she studies the World Health Organization and international cooperation during global health emergencies.