The end of a vacation is a sad occasion. The party is over, and it’s time to go back to reality. I was already fighting what you could call “The Last Day Depression” in Paris when I remembered I needed to take a coronavirus test before my flight home to the United States the next afternoon.

On Jan. 26, the Biden administration put an order into effect requiring anyone flying into the United States to provide a negative result from a coronavirus test taken no more than three days before the trip, regardless of vaccination status. Alternatively, travelers could also provide documentation that they had recently recovered from covid-19.

According to the Centers for Disease Control and Prevention, it is the responsibility of the airlines to ensure the rule is enforced. “Airlines must confirm the negative test result or documentation of recovery for all passengers before boarding,” CDC spokesperson Caitlin Shockey said in an email. “If a passenger chooses not to present a test result or documentation of recovery, the airline must deny boarding to the passenger.”

At Charles de Gaulle Airport when departing Paris, I waited anxiously for someone to ask for my test results. The Icelandair check-in line was longer than any other I saw in the terminal; I figured it was because verifying tests was slowing down the process. My boyfriend and I finally got to the front, handed our passports to the airline employee and waited for our test results to be requested.

But they never were. The employee asked about our vaccine status, checked my bag and gave us our boarding passes. Maybe someone would check before we boarded the flight? No. Maybe someone would check during our layover in Reykjavik? Also no. Maybe when we landed at JFK? Still no.

Here’s what is supposed to happen: When a traveler arrives at the airport, an employee of the airline is responsible for checking the coronavirus test results of passengers before they get on the plane. That may be at the check-in counter or sometimes at the gate. Some travelers are asked to upload their test result to apps such as VeriFly, then airline staff will review them before boarding.

I was bewildered. Since the inbound testing order was implemented, I had heard stories of travelers denied boarding because of testing mistakes. How did the two of us slip through the cracks? Was this happening to other travelers, too?

Courtnie Nichols, CEO of the travel agency TravelBash, has traveled extensively for work during the pandemic, including trips to Africa and Mexico. Testing was a stringent part of her time in South Africa and Botswana, so she was surprised no one asked for her coronavirus test results when leaving Mexico via Delta Air Lines. That wasn’t a one-time incident.

“I’ve been three times and haven’t been asked anything about my covid test,” Nichols said.

Some of her clients had the same experience when coming back to the United States from the Dominican Republic on American Airlines.

“Three or four of them in the group didn’t even get asked to see their covid test,” Nichols said. “There were three or four that did.”

When asked about American Airlines’s coronavirus test-result reviewing procedure, a spokesperson said in an email, “We have a process in place to guide our agents through checking COVID-19 test results and other required documentation.”

“Additionally, we recommend our customers use VeriFLY ― our partner and provider of a mobile health wallet ― wherever it is available, as a way to organize travel documentation and confirm compliance with their destination’s requirements,” the spokesperson said.

Nichols said she guesses that it all comes down to which airline employee you are dealing with that day, and that airlines are aware that people don’t want to spend hours in massive lines.

“I think they have so many things that are going on, it’s a little unorganized,” she said. “They’re just trying to get people through.”

Morgan Durrant, a spokesperson for Delta, said staff training includes curriculum on the CDC order.

“We want to be compliant,” Durrant said, adding that the airline will look into why some travelers say they’re not being asked for their test results.

The CDC and other relevant federal agencies can enforce the order by seeking criminal penalties and fines.

I got in touch with Icelandair to see if there was a reason my travel partner and I seemed to fall through the cracks coming back from France.

“Our procedure is that passengers with a final destination in the US are to show their negative test results at check-in in the origin airport,” the Icelandair spokesperson said in an email. “Passengers are furthermore required to fill out a Passenger Attestation form where they attest that they have received a negative COVID-19 test or that they have recovered from COVID-19 in the last 3 months. This form is collected by the airline and stored for two years.”

We had been given that Passenger Attestation form on our flight, and we filled it out and signed it before landing at New York’s John F. Kennedy Airport. No one collected them from either of us, though.

“With your experience in mind, we will review the procedures with our service providers at all airports to which we fly, to make sure that passengers have fulfilled all requirements in effect in their final destination,” the Icelandair spokesperson said in a statement.

For people like me who may find current travel rules and restrictions confusing, a State Department official advised me to refer to the CDC website for further advice and requirements for both vaccinated and unvaccinated travelers.

Additionally, “the Department advises U.S. citizens planning to return to a residence overseas to check the relevant Embassy or Consulate COVID-19 website and consider such requirements while making their travel plans, and to keep in mind that host government requirements can change with little or no notice,” the official said in an email.

I don’t think my case is the norm. I have heard dozens of accounts of people having their test documents checked, and even rechecked. Even Maurice Smith, a luxury travel adviser at the Eugene Toriko travel agency, has flown back from Mexico on Delta (same as Nichols) multiple times this year and was always asked to show his results.

With the threat of variants including delta, beta and lambda spreading, experts do believe it’s important to keep the inbound testing requirement, even if it’s not perfect.

“Anything you can do to suppress cases is beneficial,” said Adrian Hyzler, the chief medical officer of Healix International, a company that specializes in international security, medical and travel-assistance services.