In early March, President Donald Trump said that restrictions he placed on travel to and from China “saved a lot of lives,” a claim that grew to “probably tens of thousands” and “hundreds of thousands” by early April. But we found no support for such figures.

The few studies that have been done estimate the U.S.’ and other countries’ travel restrictions regarding China had modest impacts, slowing the initial spread outside of China but not containing the coronavirus pandemic. We didn’t find a study that looked at the U.S. restrictions alone, and we found only one non-peer-reviewed study, on Australia, that found an impact of such policies on deaths, though it has significant limitations.

Past studies, too, have found international travel restrictions could delay the path of the spread of diseases but do little to contain them.

Saad B. Omer, director of the Yale Institute for Global Health, told us he hasn’t seen any evidence to support the president’s claims. Previous studies of viruses with a reproduction number of 1.9 or higher, meaning the average number of other people one person infects, have shown the restrictions have to be very strict to have an effect, he said. Travel restrictions “can have an impact if you shut down 90% of all travel,” Omer said. But, “even then, it delays it a little bit but it doesn’t stop it.”

Omer co-authored a Feb. 3 article on why a travel ban wouldn’t stop the coronavirus.

Alex Nowrasteh, director of immigration studies at the libertarian Cato Institute’s Center for Global Liberty and Prosperity, looked at several of the same studies we examined and concluded that “by themselves, travel restrictions do little but delay the onset of a crisis mentality and shift the curve to the right rather than flattening it.”

As we have found with prior claims from the president, Trump’s assertions have progressively grown:

Trump, March 5, Fox News town hall: But as soon as I heard that China had a problem, I said, “What’s going on with China? How many people are coming in?” … [Y]ou both know that I closed the borders very early. …. You know, it saved a lot of lives. Trump, March 17, coronavirus task force briefing: We closed it down to China, the source, very, very early. Very, very early. Far earlier than even the great professionals wanted to do. And I think, in the end, that’s going to be — that will have saved a tremendous number of lives. Trump, March 24, Fox News virtual town hall: I made a decision to close off to China. … Thousands and thousands of more people — probably tens of thousands would be dead right now if I didn’t make that decision. Trump, April 7, task force briefing: And I was called all sorts of names when I closed it down to China. …. If I didn’t do it — if I didn’t do that, we would’ve had hundreds of thousands more people dying.

We asked the White House for support for the president’s claims, specifically whether there was support for his claims of “tens of thousands” or “hundreds of thousands” of lives saved. We haven’t received a response.

On Jan. 31, the Trump administration declared a public health emergency for the novel coronavirus and announced travel restrictions to and from China, effective Feb. 2. As of that date, there were nine confirmed cases of COVID-19, the disease caused by the novel coronavirus, in the U.S., though there had been very little testing. At that point, the Centers for Disease Control and Prevention had not yet sent test kits to public health labs, so all testing was done through the CDC.

Currently, the U.S. has the most confirmed COVID-19 cases in the world. As of April 10, the U.S. had more than 486,000 cases and nearly 18,000 deaths, according to John Hopkins University’s Center for Systems Science and Engineering.

Under the travel restrictions, non-U.S. citizens, other than the immediate family of U.S. citizens and permanent residents, were prohibited from entering the U.S. if they had traveled to China within the previous two weeks.

Research on the Coronavirus Travel Restrictions

As we’ve written before, a study published in the journal Science on March 6 estimated that travel restrictions instituted in Wuhan, China, where the coronavirus outbreak began, and those put in place by several countries in early February regarding China would “only modestly” affect the spread of the pandemic.

The researchers — a team from the U.S., Italy and China, led by Northeastern University in Boston — used a model to estimate the impact. The model showed that a travel ban in Wuhan “was initially effective at reducing international case importations,” but “the number of cases observed outside Mainland China will resume its growth after 2-3 weeks from cases that originated elsewhere.” It found that restrictions by other countries would have “a modest effect” if they reduced travel to and from China by up to 90%, unless those restrictions were “paired with public health interventions and behavioral changes that achieve a considerable reduction in the disease transmissibility.”

In other words, travel restrictions could delay, but not stop, the spread of the disease, and social distancing and hand-washing behaviors would reduce the transmission of the disease.

Another study published in March in the Proceedings of the National Academy of Sciences similarly found that travel restrictions and airport screenings in several countries “likely slowed the rate of exportation from mainland China to other countries, but are insufficient to contain the global spread of COVID-19.”

The researchers, mostly with the Yale School of Public Health, said that “rapid contact tracing” was “essential” to limit person-to-person spread.

The study did find that the travel lockdowns put in place in Wuhan and Hubei province lowered the daily rate of exportation of cases from China by 81.3% on average by Feb. 15. “At this early stage of the epidemic, reduction in the rate of exportation could delay the importation of cases into cities unaffected by the COVID-19 outbreak, buying time to coordinate an appropriate public health response,” the study said.

The study also found that airport screening “has only a moderate benefit” early in the epidemic, as most people — 64% — travel during the incubation period, before exhibiting symptoms.

The study, which relied on data on the outbreak in China and airline network data to make its estimates, concluded that travel restriction measures are “unlikely to contain the outbreak,” but they could delay the importation of cases, providing time for unaffected areas to prepare a public health response.

A third recent study, by researchers in China, the U.S. and the U.K., looked at both the travel restrictions and other emergency measures put in place in China only, estimating that shutting down Wuhan slowed the virus’ spread to other cities in China by 2.91 days.

The study, which was published in Science on March 31, concluded that the delay “provided extra time to prepare for the arrival of COVID-19 in more than 130 cities across China but would not have curbed transmission after infection had been exported to new locations from Wuhan.”

Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, has praised Trump’s travel restrictions on China, saying the U.S. has dealt with a lower number of cases because of the policies. At a press conference on Feb. 29, Fauci said, “If we had not done that, we would have had many, many more cases right here that we would have to be dealing with.”

The studies we cited suggest that the travel restrictions could have slowed down, but not stopped, the importation of COVID-19 in the U.S. But when we looked into this issue in early March, Dr. Jennifer Nuzzo, a senior scholar at the Johns Hopkins Center for Health Security, told us there’s no evidence to show that and some reasons that it may not be the case — chiefly, the lack of testing, particularly early on.

“[W]e weren’t seriously looking for cases in the US,” Nuzzo said.

Initially, the CDC testing criteria focused on those with symptoms who also had been to Wuhan or in contact with someone suspected or confirmed to have COVID-19. By late February, those criteria included anyone with a fever who was hospitalized with a respiratory illness. On March 3, Vice President Mike Pence announced doctors could order tests if they thought one was needed.

Also, the U.S. restrictions were limited. In February, Nuzzo said, other countries, including Japan, Singapore and Korea, had a significant number of coronavirus cases, but they weren’t subject to travel restrictions. The U.S. “would likely not have picked it up” if travelers coming to the U.S. from those countries were infected with the virus “because we weren’t using these other countries as criteria for testing,” she said.

Omer, of the Yale Institute for Global Health, echoed that, saying, “People coming from Italy wouldn’t have been stopped,” whether they exhibited symptoms or not. (Trump’s restrictions on travel from Europe didn’t go into effect until March 13.)

The ability of the virus to elude limited travel restrictions raises questions about the one study we did find that estimates an impact on deaths. The study — which hasn’t been peer-reviewed — estimated Australia’s restrictions on travel from China will lower the potential number of deaths from COVID-19 in the country over the next year. However, it didn’t consider any impact of cases coming in from other countries, saying it “illustrates the principle of travel bans and public health impact on epidemic control using China as a case study.”

The study, posted without peer review on medRxiv on March 12, estimated the travel restrictions, implemented Feb. 1, would reduce the cases and deaths by 87% over 400 days. The case and death counts are relatively low in Australia: 6,215 cases and 54 deaths as of April 10, according to Johns Hopkins University & Medicine.

Past Studies Find Delay, Not Containment

Several past studies have looked at the impact of travel restrictions on epidemics. They also have found some delay in the spread of the diseases, if the restrictions are significant, but not containment.

A 2014 review of 23 studies on the impact of travel restrictions on the spread of influenza found overall they have “only limited effectiveness,” the degree of which varied depending on the restrictions themselves, epidemic size, transmissibility of the virus and other geographic considerations. The review, published in the Bulletin of the World Health Organization, said: “In isolation, travel restrictions might delay the spread and peak of pandemics by a few weeks or months but we found no evidence that they would contain influenza within a defined geographical area.”

A 2011 study (included in the above review) on the 2009 H1N1 pandemic published in the journal PLOS One found that travel restrictions creating a 40% reduction in air traffic to and from Mexico, the origin of the influenza strain, caused a three-day or less delay, on average, in the first imported cases reaching other countries. It said that “no containment was achieved by such restrictions.” Even assuming an unlikely 90% air traffic reduction, the study said, “the resulting delay would be on the order of 2 weeks.”

A 2012 study published in BMC Infectious Diseases by researchers in Hong Kong estimated that “imposing a 99% air travel restriction” would delay the peak of a new influenza pandemic in Hong Kong “by up to two weeks.” But, “[a]ntivirals and hospitalization were found to be more effective on attack rate reductions than travel restrictions,” the study said.

It’s possible that the U.S. travel restrictions on China could have had some impact in slowing the importation of cases to the U.S. But we don’t have evidence of that, or of what that impact is, let alone evidence that “hundreds of thousands” of lives were saved, as the president claimed.

Update, April 15: This story was updated to include the video.