Despite China’s aggressive measures to try to reduce the spread of the novel coronavirus, which first emerged in Wuhan (located in Hubei Province), the epidemic has continued to grow. Reported cases have surpassed those of the 2003 SARS epidemic, which was also caused by a coronavirus. Nearly 20 countries have reported cases, some of which resulted from local transmission. U.S. health officials recently announced a ban on U.S. entry of foreign nationals who visited China in the last 14 days and implemented a 14-day quarantine of Americans returning from Hubei Province. The move came one month after Chinese health authorities first announced an outbreak of viral pneumonia now recognized to be caused by the new coronavirus. Russia and several European countries have taken similar steps.

Tempting as it may be to ban or otherwise restrict travel to keep the virus out, these measures aren’t always in our best interest. The World Health Organization (WHO) has stressed the importance of responding to the novel coronavirus with “facts, not fear.” The WHO has repeatedly said that it does not recommend that countries restrict travel or trade to prevent importation of the virus. When countries do not follow the WHO’s advice, and instead implement non-evidence-based travel bans to prevent the spread of disease, they do so in violation of the International Health Regulations – a legal framework that governs how countries should respond to international infectious disease outbreaks. Michael Ryan, executive director of the WHO’s emergency program, said in a recent news conference that if member states impose unilateral trade and travel restrictions, it is a “recipe for disaster.” Nonetheless, countries are doing just that.

These concerns are well-supported by recent history. In 2014, following two imported cases of Ebola, U.S. politicians called for a restriction of travel between the United States and West Africa. Several states announced plans to place returning Ebola health workers into mandatory quarantines. In some instances, these efforts were done at the direction of governors who, to appear engaged and decisive in responding to the situation, overruled more nuanced guidelines issued by state health officials. Medical and public health experts involved in the efforts to contain the spread of Ebola at the source strongly cautioned against such measures, stressing that it was likely to interrupt the transport of clinical volunteers and supplies that were essential to the Ebola response. Organizations involved in the Ebola response noted that threats of quarantines caused a decrease in the number of doctors and nurses who volunteered to treat Ebola patients in West Africa.

Ultimately, political pressures to implement travel bans were stemmed by the hasty deployment of a program to track and monitor the health of returning travelers from West Africa. State and local public health departments were asked, with minimal notice, to figure out how to screen and monitor thousands of returning travelers daily. Though this effort was largely seen by the medical and public health community as preferable to mandatory quarantines, health officials reported that it was costly and diverted resources from other public health priorities. In the end, health officials monitored close to 30,000 individuals but identified no Ebola cases.

Restrictive travel and trade measures have worsened the social and economic tolls of past events. During the 2009 influenza pandemic, U.S. politicians called to close the southern border and suspend travel from Mexico. Were such measures implemented, they probably would not have helped: The virus was already well-established in the United States and spreading quickly. But politicians’ fixation on the geographic origins of the pandemic did not ultimately serve the United States well, when countries began quarantining planes from North America in an ultimately futile effort to keep out the new flu virus. Additionally, more than 20 countries announced bans on U.S. pork imports in the mistaken belief that the virus could be spread by pigs, causing an estimated $1 billion in economic losses.

Banning travel from China is unlikely to keep the new coronavirus out of the United States, especially as the geographic footprint of the epidemic continues to rapidly expand. This virus is simply moving too quickly and spreading too quietly for us to assume that we know where in the world all cases are. The current approach in most countries to finding cases is to screen travelers with connections to Wuhan or greater China. Though these efforts are helping to educate travelers and improve our surveillance for cases, they are by no means able to keep all cases of the virus out of a country because we will not find cases that originate elsewhere. It is increasingly likely that the virus will spread from other parts of the world, and there could already be additional unrecognized cases in the United States.

Even if it were feasible to keep coronavirus out through travel bans, these measures can make us less safe. Travel bans can penalize countries that report cases, which may in turn reduce countries’ willingness to share information about their outbreaks. Travel bans may also interrupt the flow of essential supplies upon which we depend to control the epidemic. China is a large producer of critical medicines and personal protective equipment – it is in our best interest to stay positively engaged with China in responding to this epidemic. In recent days, Chinese officials have criticized the U.S. response as “unfriendly.”

With increasing signs that the new coronavirus epidemic has grown beyond the point of containment, it is time to think about how best to mitigate its impacts. If leaders use their influence in support of evidence-based measures, rather than ones that risk increasing the social and economic tolls of the epidemic, it will be helpful to the coronavirus response. Governments must resist the temptation to ban travel from affected areas, while also working with airlines to ensure that their decisions to cancel flights don’t disrupt the transport of essential goods and prevent epidemic responders from traveling to where they are needed. Political leadership is needed to expedite the development of diagnostic tools, vaccines and therapeutics to diagnose, treat and prevent additional infections. U.S. hospitals and health departments will need additional resources to respond to the growing number of coronavirus cases in the United States. Each of these actions will require funding and bipartisan political support to pass supplemental funding legislation. Let’s focus on what we know works, rather than what is more likely to harm.

Jennifer B. Nuzzo is an epidemiologist with the Johns Hopkins Bloomberg School of Public Health’s Center for Health Security.