Rival financial hubs Hong Kong and Singapore are set to become the first regions in the world to open a reciprocal “air travel bubble,” after ministers from both governments announced a preliminary agreement on October 15. Under the deal, residents from either city would be able to travel to the other without undergoing quarantine—so long as they test negative for COVID-19.

“This is a milestone in our efforts to resume normalcy while fighting against the long-drawn battle of COVID-19,” Hong Kong Secretary for Commerce and Economic Development Edward Yau said. Full details of the arrangement are still being hashed out, but Yau has “every confidence” the plan can “come to fruition very soon.”

Previous "travel bubble" hopes have not lasted long.

Governments have floated the notion of opening travel bubbles since at least May—when Australia and New Zealand were mulling the idea. But the concept has so far proven too optimistic as sudden spikes in local case numbers put travel plans on hold.

At best, countries have implemented unrequited quarantine exemptions. On October 16, for example, Australia welcomed passengers from New Zealand without quarantine, but New Zealand still requires all tourists to undergo a two-week isolation.

The Kiwi nation has kept COVID-19 largely under control, with daily case numbers mostly in single digits since May.

Hong Kong and Singapore haven’t been out of the woods quite so long.

But Singapore Transport Minister Ong Ye Kung says that both Hong Kong and Singapore have “low incidence” of COVID-19 cases and have “robust mechanisms” to manage outbreaks. “This has given us the confidence to mutually and progressively open our borders to each other,” Ong said.

On October 15, Singapore reported three new coronavirus cases, completing four days of single digit growth. The same day, Hong Kong reported 12 COVID-19 cases—the highest single day rise in a week. Although those numbers are low compared to many other places, Hong Kong’s hyper vigilance makes even a spike of 12 cases cause for concern.

Just last week, Secretary for Health Sophia Chan floated the idea of enforcing mandatory COVID-19 tests as some experts warned of a possible “fourth wave” of infections following a daily increase of 18 cases.

Last month the city tested close to 2 million people to counter its third wave, which experts blamed on Hong Kong’s previous quarantine exemptions. Those exemptions waived the 14-day isolation period for certain groups, such as sea and air crew members.

“I think the risk posed to Hong Kong by travelers from Singapore would be minimal,” says Hong Kong University epidemiologist Ben Cowling, citing the city’s low case numbers. “But it would still be important to arrange testing for travelers from Hong Kong or Singapore either shortly before departure, or to arrange testing on arrival.”

The travel bubble could ease financial strain on airlines and the tourism industries of both cities. Shares in Hong Kong's flag carrier Cathay Pacific closed up 6% on the news on October 15 after making its biggest gains in seven weeks.

The route between Hong Kong and Singapore is normally the 17th busiest in the world, with Hong Kong tourists accounting for 3% of all visitors to Singapore last year. This year, of course, that flow came to a near halt. In Hong Kong, visits from Singapore dropped over 93% in the first eight months of 2020.

Under the preliminary agreement, travelers will be required to obtain a negative COVID-19 test from a facility recognized by both Hong Kong and Singapore governments. Airlines will also have to run dedicated routes—not allowing for transit passengers—and group tours will not be allowed.

Hong Kong’s government last month said it hoped to open travel bubbles with ten other countries, including New Zealand, Vietnam, South Korea, Germany and France.

But with social distancing measures still enforced in Hong Kong—limiting dining groups to four people, closing public beaches and cancelling public events—many of the usual tourist activities will be off-limits when travelers arrive.