Tonga’s most populous island Tongatapu has implemented a nighttime curfew and closed nonessential businesses as part of a seven-day shutdown after confirming its first case of Covid-19.

The man, a youth missionary with the Church of Jesus Christ of Latter-day Saints, was among 215 passengers on an Oct. 27 repatriation flight from Christchurch, New Zealand, a church spokesperson confirmed.

He was fully vaccinated, did not show any symptoms and had twice tested negative before boarding the flight, but he had a “weak positive” result on a Covid test taken after arrival, health officials said. All other passengers tested negative.

With a population of just over 100,000, Tonga has remained closed off to foreign nationals since the pandemic began on March 2020. Health officials say 62% of the population is vaccinated.

The infection was confirmed after the man tested three times as required the day after arriving at the capital, Nuku’alofa. The person was a “weak positive,” said Ministry of Health chief executive Dr. Siale ‘Akau’ola.

The patient will be tested again on Friday.

“It could be due to this person being fully vaccinated and the virus is struggling to grow, or this person had contracted Covid-19 before,” ‘Akau’ola told the news site Matangi Tonga.

“It’s better we just identify it as positive now and go into lockdown as a precaution, rather than to regret it later when it’s too late,” he added.

All staff who came in contact with the case also had negative tests.

The other passengers were to be tested three times over the remainder of their 21-day quarantine at Tanoa Hotel, which was guarded by Tongan military.

Meanwhile, Tongatapu implemented an 8 p.m. to 6 a.m. curfew, limited public services, closed nonessential businesses and enforced social distancing and home isolation for seven days starting at midnight Monday.

The young Mormon missionary was returning from a mission in Africa and had spent several weeks working in New Zealand before being able to return to Tonga. Everyone who had been in contact with the young man had tested negative, according to the church spokesperson.

Thousands thronged vaccination sites after the news of the country’s first positive case over the weekend.

About 86% of the population has had at least a single shot, Minister of Health Dr. ʻAmelia Tuʻipulotu said.

Japan donated almost 40,000 Oxford-AstraZeneca vaccines to Tonga earlier this year, while 31,600 New Zealand-donated Pfizer vaccines arrived in Nuku’alofa on Oct. 20.