(Bloomberg) -- Hong Kong tightened its travel curbs for residents returning from 16 places -- including the U.S., France and Spain -- less than two months after it started easing its strict quarantine measures, in a reversal that reflects a fear of reopening as the delta variant drives resurgences across the world.

Fifteen countries were moved from the “medium-risk” to “high-risk” category, which means that vaccinated residents returning from those places from Aug. 20 must spend 21 days in hotel quarantine upon arrival, while tourists and unvaccinated residents are no longer allowed entry, said a government statement Monday.

Previously, residents and tourists with antibody test results proving they had been vaccinated had to spend only seven days in hotel quarantine.

The about-turn comes after a resident returning from the U.S. tested positive for the virus several days after completing a seven-day quarantine, sparking fears that the eased travel rules would allow the delta variant to slip into the Asian financial hub. Hong Kong has enjoyed a streak of over two months with nearly no local virus cases even as neighbors like Singapore and mainland China struggle with the mutation, but its vaccination rate is lower than in other developed economies.

“The global Covid-19 epidemic situation is under serious threat from the delta variant, with acute surges in the number of confirmed cases within a short period of time in many countries,” the statement said, adding that the measures were meant to “uphold the local barrier against the importation of Covid-19.”

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