NEW YORK (AP) — In the weeks before President Donald Trump spoke from the Oval Office to announce restrictions on travelers from more than two dozen countries in Europe, thousands of people from the region already had stepped off planes at U.S. airports, and an untold number of them carried the coronavirus.

The same can be said of flights from China in the weeks before the U.S. clamped down on those. Thousands who visited the country where the illness began had entered the United States without any kind of health review.

Such sobering realities highlight just one element of the federal government's shortcomings in getting ahead of the virus and halting its spread from overseas travelers.

A day-by-day review of the spread of an unfamiliar virus from its earliest days shows U.S. officials have often been slow to respond or steps behind, with critical gaps in containment measures such as travel restrictions and airport screenings that allowed the crisis to grow to more than 2,100 infections and 51 deaths.

“There have been gaps in the way the U.S. has approached its response, which has not been comprehensive enough to contain the virus at the early stages of the epidemic,” said Josh Michaud, associate director of global health policy with the Kaiser Family Foundation in Washington.

That was evident from the very beginning of the coronavirus outbreak in the U.S. On Jan. 15, a 35-year-old man returned home to Washington state through the Seattle airport after traveling to Wuhan, China, where the virus was already spreading. He would become the nation's first known case. Shortly before, on Jan. 13, a woman in her 60s arrived home through the Chicago airport after traveling to Wuhan. She would be Chicago's first known case.

Both of those travelers came to U.S. days before the federal government began screenings for passengers who traveled through Wuhan at three U.S. international airports, New York's Kennedy, San Francisco and Los Angeles. That list was expanded on Jan. 21 to include hubs in Chicago and Atlanta. Seattle-Tacoma wouldn’t be added to the list until Jan. 28.

Also, there's no guarantee those screenings — which involved passengers filling out health forms and having their temperatures taken — would have caught those early patients, who didn't report symptoms until later. U.S. researchers say screenings may miss half of COVID-19 infected people, since they may not develop symptoms for several days.

By Jan. 24, both the Chicago woman and Washington state man had sought medical care after feeling sick, and tests confirmed they had the virus. Learning of the two early cases, public health workers scrambled to reach hundreds of people who may have been exposed to them on flights and on the ground, knowing they wouldn't be able to find them all with certainty.

With infections in Wuhan multiplying at an alarming rate, the White House announced on Jan. 31 that non-residents who had recently been to mainland China would no longer be allowed entry.

Americans returning from the Wuhan region would be subject to a mandatory two-week quarantine. In Boston, a man who would become the city's first case had returned after traveling to Wuhan just days earlier.

By mid-February, cases in China had pushed past 44,000. But the threat still seemed low in the U.S. and the Dow Jones Industrial Average closed at its highest point ever amid investor optimism the trade wars initiated by Trump were being resolved.

Then on Feb. 24, a teenager at Jackson High School in Mill Creek, Washington, stayed home with fever, body aches and a headache. He was tested for flu at a clinic that week, but the test came back negative. Feeling better, he went to school on Feb. 28. Arriving on campus, he got a call to come home immediately. It was COVID-19.

The next day, Trevor Bedford, a Seattle scientist, tweeted about the “enormous implications” of finding genetic fingerprint similarities between the teenager's virus and the Washington man who became the first known U.S. case. “This strongly suggests that there has been cryptic transmission in Washington State for the past 6 weeks," he wrote on Twitter.

To some, containment still seemed like a possibility in the United States, which as recently as about two weeks ago had no deaths and just 60 known cases, mostly people who were under federal quarantine after being evacuated from China or a cruise ship in Japan.

“It may get a little bigger; it may not get bigger at all,” Trump said in a national TV address at the time.

With cases rising above 1,000 in Italy and 3,000 in South Korea, the White House announced on March 1 that U.S.-bound passengers would undergo screenings before leaving those countries. But travelers from Italy who would eventually test positive were already on their way.

On March 4, California health officials announced that three of its six new cases were people who had visited northern Italy. A day later, Illinois announced its fifth confirmed case — a man who had recently returned from Italy. A day after that, Oklahoma announced its first case — a man who had returned from Italy about two weeks earlier. And a few days later, the state announced its second case had also traveled to Italy.

By the time Trump announced the European travel ban Thursday, cases in the region including Italy, Spain and France had mushroomed to more than 17,000. When a similar ban was announced on people traveling from China, that country had around 11,000 cases. Iran had about 600 confirmed cases when the U.S. banned travelers who had recently been there.

“The European Union failed to take the same precautions and restrict travel from China and other hotspots,” Trump said. “As a result, a large number of new clusters in the United States were seeded by travelers from Europe.”

Saturday, Trump closed some glaring exceptions to his European travel ban, adding the United Kingdom and Ireland to the list and considering imposing travel restrictions within the U.S. as well. His decision came as deaths in Britain doubled from the day before to 21, and infections rose from 800 to over 1,100.

Some experts question the effectiveness of any kind of travel restrictions given the heavy volume of global travel. Last year, for example, 4.2 million passengers arrived in the U.S. on flights from China and 2.2 million from Italy.

Holes in the containment net may sound alarming to the general public, but experts in controlling outbreaks assume the net will let some slip through. The point is to slow down or “flatten” rates of infection to keep the number of severely sick patients from overwhelming hospitals, which aren't big enough to accommodate a surge.

"We are essentially spreading this spread over a longer period of time to allow health systems time to adapt and respond," said Dr. Sandro Galea an epidemiologist at Boston University.

The benefit of stopping a portion of new infections from entering also depends on how aggressively officials are simultaneously controlling infections already within their borders, said Benjamin Cowling, an epidemiologist at the University of Hong Kong.

But nearly two months after the first U.S. case was confirmed, the persisting lack of testing capacity has left experts uncertain about how many more infected people aren’t being identified. Some researchers say the true count of infections in the U.S. may be upwards of 14,000..

“It is a failing, let’s admit it,” said Dr. Anthony Fauci of the National Institutes of Health on Thursday of the testing limitations.

Most people who get infected with the virus experience moderate symptoms. and the vast majority of people recover. Others, including older adults and people with existing health issues, can become severely sick.

Patricia Herrick, the daughter of an 89-year-old woman who died last week in the Seattle-area nursing home that has become ground zero of the U.S. outbreak with at least 25 deaths linked to it, said testing should have started much earlier so the sick could be separated from the well.

“We let this thing advance so far. We didn’t take this seriously enough,” said Herrick, whose mother was never tested for COVID-19. “I don’t know that she would still be living. ... It's tragic."

Kaiser’s Michaud acknowledged government health officials may have been “flying blind at first” but the inability to test and identify cases has put them behind.

“We’re trying to catch up. But we can’t catch up at this point.”

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Johnson reported from Seattle.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.