Photo/Illutration Staff members of a U.S. travel company arrive at Narita Airport on May 24 to take part in an experimental tour. (Shinya Matsumoto)

The decrease in testing at Japan’s ports of entry has naturally led to far fewer positive COVID-19 results, but some health experts warn that asymptomatic arrivals could be slipping through on a daily basis.

And the big concern is that they may be carrying a new and potentially devastating strain of the novel coronavirus.

According to the health ministry’s data, the daily average number of people who tested positive for COVID-19 upon arrival in Japan was around 92 in May, when tight border measures were still being applied.

The highest figure for the month was 142 recorded on May 9 and the smallest was 48 on both May 3 and 4.

The dates refer to when the ministry published the numbers, not when the test results were known.

The daily cap of people allowed to enter Japan was 10,000 in May.

The government doubled the cap to 20,000 on June 1, when it started exempting travelers from 98 “safe” countries or regions from having to take COVID-19 tests and quarantining after arrival.

The number of positive tests at ports of entry has significantly dropped since then, with the highest daily number so far at 14, on June 4.

People traveling to Japan must show a negative result for a PCR test taken within 72 hours before departure.

The ministry’s statistics for both months show that these passengers could still be carrying the novel coronavirus on their way to Japan.

If the positivity level among arrivals in May has carried over to June, more than 100 infected people could be entering Japan on a daily basis without being tested.

According to some estimates, around 80 percent of new arrivals will be exempt from testing in Japan because of the June 1 change.

Yoshiaki Katsuda, professor of travel medicine at Kansai University of Social Welfare, said Japan should not worry too much if a new Omicron variant is found overseas that is more contagious but has the same pathogenicity as existing variants.

But if such a new Omicron variant is more likely to cause serious symptoms, it “would be a different story,” he warns.

“It’s important to keep abreast of information on Omicron variants, and to change testing and quarantining systems at ports of entry (if a dangerous strain is found),” he said.

The ministry’s data showed, through genome analyses conducted by June 1, that 314 arrivals were infected with a new Omicron subvariant known as BA.2.12.1, which could be more contagious than BA.2, the currently dominant strain in Japan.

The analyses also found that 18 arrivals were infected with BA.4 and 25 with BA.5, both Omicron subvariants.

For business travelers, employers can monitor their movements through checks of their itineraries in Japan. But it may be difficult to monitor foreign tourists, who will be allowed to enter the country from June 10, that way.

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The Asahi Shimbun