A study conducted earlier this year shows that there may be a way to reduce the number of Covid infections on board commercial aircraft to practically zero.

The results of the study were published in a peer-reviewed article published September 1 in the medical journal Mayo Clinic Proceedings. The article – a joint effort by the Mayo Clinic, the Georgia Department of Public Health, and Delta Air Lines – showed that a polymerase chain reaction (PCR) test performed within 72 hours of the flight reduced the rate of infected travelers on board to 0.05 % decreased. That’s five people for every 10,000 passengers.

At the time of the study, the infection rate in the US was 1.1% – or about 1 in 100 people.

“A damn low number”

The results analyzed data from Delta’s preflight testing program, which ran from December 2020 to May 2021.

This is how Delta’s test program worked: Passengers on selected flights from New York City and Atlanta could fly to Italy without quarantine if they were tested negative for Covid-19 via a PCR test before departure and within 72 hours before the flight a rapid antigen test on landing.

Data from Delta’s preflight testing program provides new information on test feasibility, test accuracy and infection rates among passengers on commercial flights.

Mario Tama | Getty Images News | Getty Images

Of the 9,853 people who tested negative using the PCR test, four tested positive using rapid antigen tests at the airport. The diagnoses were confirmed by a rapid molecular test and these people were not allowed to fly.

Of the passengers who flew to Italy, one tested positive upon landing.

That equates to one case detection per 1,970 travelers “during a period of high prevalence of active infections in the United States,” the article said.

“That’s a hell of a low number,” said Dr. Aaron J. Tande, the article lead author and an infectious disease specialist at the Mayo Clinic in Rochester, Minnesota.

The study suggests that a PCR test within three days of the flight makes subsequent tests at the airport largely superfluous, especially in combination with mask requirements on board and increasing vaccination rates for passengers.

‘Limits of the Study

The journal article mentions several “limitations” that may have affected the study’s findings, including the role of preflight testing in travel behavior. Participants suspected of having a Covid infection may have decided not to travel. Others may have been more careful wearing masks and self-isolating knowing they had to test negative to fly, Tande said.

“I can’t say that made the number of positive tests that low – or really did it make the 72-hour test that good,” he told CNBC. “But … the bottom line is that it’s a safe flight for people, and that’s what we want.”

If you were to repeat the study now … I think you would see a significant decrease in the rate of infection on board. “

DR. Aaron J. Tande

Mayo Clinic

Tande said the results are based on the Covid-19 strains that were circulating in the United States in the first half of 2021, rather than the more contagious Delta variant that is now dominating.

“I don’t think you could say you would get the exact same result by repeating the study now – with a different infection rate in the community and a different virus,” he told CNBC. “I think you would see a significant drop in the rate of infection on board.”

Safer but less workable options

The pilot took into account five testing strategies, two of which may have detected even more infected flyers.

For example, a single rapid molecular test at the airport could have found more infections because it minimizes the time between test and flight and so could capture infections that occur during that time. Adding a 72 hour PCR preflight test would likely find even more, according to the study.

Although airports weren’t designed for large-scale medical testing, many have set up makeshift facilities over the past year, like the Rome Fiumicino International Airport shown here.

Alessia Pierdomenico | Bloomberg | Getty Images

However, a preflight PCR test is the “better approach” because it is more feasible, said Tande. PCR tests are widespread, “more sensitive” – ​​which means they can better detect positive cases – and they are taking test logistics away from airports, he said. Preliminary tests also give infected travelers time to reorganize their plans rather than surprise them just before departure.

Test flights or vaccinated flights?

Preflight PCR testing can make flying safer, but most passengers now fly without one. And the airlines are silent when it comes to signing them in the future.

However, tests could become the de facto rule on international flights if the countries of arrival require them for passengers to enter. A Delta Air Lines spokesman declined to say whether it would require testing for its passengers, but said that “each country’s government is responsible for setting its own requirements”.

Tande said he would feel safer on a flight that required passengers to pass PCR tests before the flight. However, if given the choice, he said he preferred one more vaccination flight.

“I would definitely take the vaccinated flight – and (I would) mask,” he said.

Qantas CEO Alan Joyce said last week that passengers must be vaccinated on its international flights, according to news.com.au. US officials are currently debating whether to make vaccinations mandatory at home and abroad, the Washington Post reported this week.

“Unfortunately, Covid will be with us for a long time due to the discontinuation of vaccinations,” said Tande. “By continuously masking and testing before flying … we can improve safety so that we can continue to function as a normal society.”