When Singapore announced the start of quarantine-free travel to certain countries including the U.S., U.K., France and Canada, Singapore Airlines Ltd.¡¯s website crashed and ticket prices shot through the roof.

Expatriates scrambled to book trips home in time for Christmas, while cooped-up locals jumped at the chance to finally get off the tiny island. With domestic virus curbs extended recently after a surge of infections, the well-heeled are ever-more desperate to take flight.

Left behind by this exodus are more than half a million domestic and migrant workers, many of whom haven¡¯t seen their families in years. Thousands live in cramped dormitories ¡ª some, according to recent claims, in unsafe and unsanitary conditions.