Can preflight testing get people flying again?
The International Air Transport Association (IATA) thinks so. Last month, the trade association, which represents some 290 airlines around the world, called for the "development and deployment of rapid, accurate, affordable, easy-to-operate, scalable and systematic" Covid-19 testing for all passengers as a way to restore passenger confidence, bypass quarantines and reopen borders.
Within weeks, United Airlines, American Airlines and JetBlue announced plans to launch preflight testing programs to places such as Hawaii, Costa Rica and the Caribbean, depending on the airline.
By that time, Italy's largest airline, Alitalia, was already operating two flights between Rome and Milan for passengers who tested negative before boarding.
Panama reopened its borders this week to travelers who arrive with a negative Covid-19 test in hand, or who test negative after taking a rapid test upon landing.
But testing isn't quite that simple. Just ask Iceland.
When Iceland reopened on June 15, the country exempted travelers from a two-week quarantine if they tested negative for Covid-19 upon arrival. Cases started rising less than a month later.
In August, Iceland revised its policy. It now requires two Covid-19 tests — one upon arrival and another five days later — with mandatory quarantining in between.
In one of the most high-profile testing fails of the pandemic, a Covid-19 outbreak erupted at the White House this month due in part to its practice of relying on rapid tests to screen visitors. The tests are known to miss up to a third of asymptomatic infections.
In calling for preflight testing last month, the IATA said that "deployable solutions are expected in the coming weeks." Medical experts say that may be premature.
Polymerase chain reaction tests, also called PCR, can more accurately diagnose positive cases, said Dr. Peter Gulick, an infectious disease expert at Michigan State University. But those tests, which rely on a nasal swap, throat swab or saliva, "are run in a lab so it may take days to come back, and a patient may get infected during that time," he said.
That is the rub with PCR tests. Test too early, and a person's chances of being infected after the test increase. Test too late, and the results may not be ready by departure time.
Rapid antigen tests can solve the timing problem, but "they can result in 20% to 40% false negatives," said Gulick. That makes those tests better suited to confirm infections, rather than to give an "all clear" indication of no infection.
Rapid PCR tests exist, but their production hasn't yet matched demand, said Dr. Shira Doron, infectious disease physician and hospital epidemiologist at Tufts Medical Center.
"At this time, there are a few companies making rapid PCR tests," she said. "These are sensitive and have few false positives."
Research conducted by IATA shows that 65% of travelers believe people who test negative for Covid-19 should not be required to quarantine. Health care professionals, however, aren't so optimistic.
"A preflight test, even when given at the security checkpoint, is not a foolproof protocol to prevent the spread of Covid-19 to the passenger's destination site," said Dr. Makeda Robinson, a virologist at Stanford University.
Robinson said every person infected with Covid-19 has an incubation period when the virus can't yet be detected by tests. The average is four to seven days, but it can run as long as 14 days in some people, she said.
"For comparison, with the 2003 SARS virus, people tended to be most infectious after they developed symptoms, making it easier to identify cases and separate them from the unexposed population," she said. "However, SARS-CoV-2 [Covid-19] has more asymptomatic infections and can be highly infectious prior to symptom onset."
"This means that someone could be infected, … have an initial test which was negative prior to boarding the plane, and then test positive in the days following their flight," Robinson said.
Without an effective vaccine, traveling without a quarantine period will likely enable Covid-19 cases to continue spreading, said Robinson.
"A potential middle-ground approach could include a preflight test with a shorter quarantine period of around seven days in the destination country and follow up [with a] post-flight test," said Robinson.
The trend right now is to eliminate quarantines though. Starting Nov. 1, the Bahamas is removing its 14-day "vacation in place" quarantine requirement in favor of a "triple testing" policy. Incoming travelers must obtain a PCR swab test no more than seven days prior to travel, followed by a rapid antigen test upon arrival, and another 96 hours later.
Starting Oct. 15, Hawaii will allow passengers on certain United and American Airlines routes to avoid a 14-day quarantine if they test negative through the airlines' new testing programs.
"A test represents only a moment in time," said Doron. "Someone can be negative one moment and develop the disease the next. Although [testing] decreases the likelihood that someone with Covid-19 will board a plane, it does not eliminate the risk."
That may be enough for places that are battling active coronavirus outbreaks within their own populations.
But a single preflight test will likely not convince countries that have few or zero new cases — such as New Zealand, Taiwan, Thailand and Singapore — to open their borders anytime soon.