COVID-19 has officially been a pandemic since March 2020, marking the date when the disease finally became a worldwide problem. But just because it was everywhere didn’t mean it was everywhere – there were a few countries that held on for a surprisingly long time without a single case.

And by “a surprisingly long time”, we mean until today. The small island nation of Tonga, about 2000 kilometers northeast of New Zealand and 5000 kilometers southwest of Hawaii, has today reported its first-ever case of COVID-19 – leaving just Kiribati and Tuvalu in the elite club of countries that have so far escaped the virus.

Like many nations, travelers into Tonga have been required to quarantine for a period of time after entering the country – and this first and so far only case of COVID-19 on the island shows exactly why. The disease was brought in on a flight from Christchurch, New Zealand, the country’s Prime Minister Pohiva Tu'i'onetoa announced on Friday, and didn’t test positive until a day into their quarantine period.

If the traveler had not been caught by quarantine restrictions, the effect could have been devastating. Just look at Fiji – another island nation less than 800 kilometers away from Tonga. By the end of March 2021, the 900,000-strong population had seen just two deaths from COVID-19 and only 70 cases overall. But in April, the Delta variant tore through the islands, infecting over 50,000 people and killing at least 673.

In response, Fiji mounted a massive vaccination drive, and now has 70 percent of the population at least partially vaccinated. But Tonga’s rate of vaccination is much lower: less than half of Tongans have received one shot, and the nation is highly reliant on the COVAX program and donations from richer nations such as New Zealand.

Immunologist Dr Dianne Sika-Paotonu told New Zealand news outlet Stuff that the case was “heart-breaking.”

“Tonga has been one of a group of countries within the Pacific region that has managed to protect its people by keeping the virus out of the country for so long,” she said. “If this case is not contained, the potential consequences for the Tongan nation will be catastrophic.”

That the infection made it to the country at all is kind of mind-boggling – and a stark reminder against letting our collective guard down too much while the pandemic rages on. The city of Christchurch had previously been COVID-19 free for months thanks to New Zealand’s quick and uncompromising pandemic response, and the traveler who unwittingly brought the virus into Tonga had received both doses of the Pfizer vaccine and tested negative before their flight.

By the time news came out that four cases had been reported in the city, the flight was already on its way to Tonga. The infected passenger, Sika-Paotonu told Stuff, “likely indicates more Covid-19 spread in the Christchurch community than is being currently reflected.”

While Tonga’s first ever COVID-19 patient recovers, the other 214 passengers, as well as all the health staff, police officers, and airport staff, are now living in quarantine until the potential for infection is past, Tongan Health Ministry chief executive Dr. Siale ’Akau’ola said. Tongans have been advised by the prime minister to practice social distancing and follow curfews in preparation for further announcements this weekend.