Tonga records its first Covid case.

For nearly two years, the remote Pacific island of Tonga has avoided the global pandemic that has infected hundreds of millions of people and left millions dead.

That streak of good fortune ended on Friday, when the island nation recorded its first coronavirus case.

The infected person arrived in Tonga on commercial flight that left Christchurch, New Zealand, on Wednesday, the Ministry of Health in New Zealand confirmed in a statement. Christchurch has reported four active community cases in the last two days.

The ministry said the individual had been fully vaccinated, and had tested negative for the virus before travel. But a routine test after arrival, on Thursday, returned a positive result the following day. New Zealand health officials are working with Tonga to confirm the case.

Tonga’s geographical isolation — the island is 1,100 miles northeast of New Zealand — has helped it to avoid the virus until now, even as nearby Fiji fought what at one point was among the world’s fastest growing coronavirus outbreaks.

Tonga’s prime minister, Pohiva Tu’i’onetoa, has warned islanders to prepare for the possibility of a lockdown if more cases emerge, according to the Tongan news website Matangi Tonga, which said that he was expected to make an announcement on Monday.

After the positive case was confirmed, Dr. Siale ’Akau’ola, the chief executive of Tonga’s health ministry, said all the health workers, police officers and airport staff who were on duty when the plane arrived had also been put into quarantine as a precaution.

Around 32 percent of Tongans are fully vaccinated against Covid-19 and 49 percent have had at least one dose of a vaccine, according to Our World in Data.