For the rest of this year, passengers arriving at Finland’s Helsinki Airport will be able to get quick, apparently very reliable coronavirus tests from…dogs.

It’s one of the biggest trials so far in the use of dogs to sniff out SARS-CoV-2; a similar test has been underway for a month at Dubai International, and already published research from Germany indicates dogs have a detection rate of around 94% for the virus.

In the Finnish trial, which began September 23, four canines are being used—two at a time; they tire easily—though the University of Helsinki researchers behind the scheme say they have 10 that have been trained and can be relied upon to work in a noisy airport environment that is full of different smells.

Passengers are invited to take simple sweat swabs from their own skin using sterile tissue (the Dubai trial involves sticking plastic tubes into people’s armpits), then drop the tissue into a jar that is passed through a hole in the wall to the waiting dog. The test takes a few seconds. The subjects are then asked to take a standard polymerase chain reaction (PCR) test for the coronavirus, so comparative data can be gathered for the study.

If the canine test comes back positive, “we take them by the hand and see 100% that they go to the PCR test as well,” lead researcher Anna Hielm-Bj?rkman told Fortune. People arriving in Finland with the coronavirus are encouraged to self-isolate, though the country has no heavily enforced quarantining system for such cases.

“So much more sensitive”

The trial began September 23, and early in the European afternoon around 50 tests had already been conducted. Hielm-Bj?rkman said the team expected to conduct around 100 tests a day and to see around one positive case in every 500 tests.

“It finds all the positives that the PCR finds and then [around] 5% more positives than the PCR. The dog is so much more sensitive,” she said. “It finds more positives where people have had the disease and still have the virus in their body, even though they’re not contagious anymore. Also what it’s able to [do] is it can find the positive ones up to one week before they get their clinical symptoms.”

If the dogs are so sensitive that they can detect the virus in people who have passed through the contagious stage, is that not overdoing it?

Not a problem, said Hielm-Bj?rkman: “Some PCR tests do the same thing…The reason we haven’t changed the cutoff point yet is there is really no research yet on how long people are contagious. We will let the dogs tell us [that very small amounts of the virus have been detected] until there is enough science to back up a cutoff point. Then we’ll teach them again: ‘If it’s lower than this, you don't need to tell us.’”

Hielm-Bj?rkman's team has been conducting preliminary tests since April, and first announced success in May. Although it has not yet produced any peer-reviewed paper about its findings—or indeed submitted an article for peer review—she said the urgency of the situation had led the team to move straight to this pilot.

“We know the dogs work,” she said. “We’ve been doing this research for five years before, training them [to detect] cancer and other diseases. We thought in this time of an epidemic, the most important thing for Finland at the moment is getting these good tests. Dogs are superior to PCR tests. It’s totally backwards, but in a time of COVID, knowing it takes three months to get something peer reviewed, we went operational before we had a peer-reviewed article.”

Instilling confidence

In theory, the technique being used at Helsinki Airport could be formally rolled out quite quickly. However, a scenario involving dogs sniffing passengers up close, rather than sniffing their samples in another room, would require a legislative change in Finland—this would be relevant in settings such as the entrance to a concert hall, where the dogs would operate like traditional sniffer dogs, Hielm-Bj?rkman said.

The aviation sector, which has been hammered by the COVID-19 pandemic, is desperate to get people back on flights. Testing is crucial both for passenger confidence and for the confidence of border authorities, and—given the volume of passengers passing through large airports—speed is of the essence.

Also on September 23, Reuters reported that Lufthansa is talking to drugmaker Roche about the deployment of antigen tests—a faster and cheaper alternative to PCR tests—that produce results in 15 minutes or so (PCR tests take hours).

Alitalia is even running special flights between Rome and Milan that are reserved for passengers that have had negative antigen tests, indicating that they do not have the virus in their systems.

But antigen tests are known to produce more false negatives than PCR tests. It appears the smell-based technique is more reliable, and even quicker in producing results. It’s a test that can be automated—a French hospital is preparing to deploy an enormous and very expensive Breathalyzer, originally designed for atmospheric science, to get results within seconds—but sniffer dogs are smaller, cheaper, and already widely available.