Taipei, June 14 (CNA) The Central Epidemic Command Center (CECC) on Monday announced tightened quarantine rules for flight crew members who are unvaccinated against COVID-19, as well as mandating antibody tests for those who are fully vaccinated.

The new measures, which took effect on June 12, require flight crew on long-haul flights who have not received any COVID-19 vaccine shots to be quarantined for five days upon returning to Taiwan and get a polymerase chain reaction (PCR) test on their last day in quarantine.

They will then have to follow "enhanced self-health management" rules for nine days, during which they will not be permitted to take public transportation or visit crowded areas.

During that period, they will also be required to keep a record of their daily activities and everyone with whom they come into contact, and get two rapid tests for COVID-19, the CECC said.

These same rules apply to those who received their first dose of a COVID-19 vaccine within two weeks of their flight assignment.

Quarantine rules for this group will be further tightened on July 1, with a mandatory quarantine of seven days upon their return, followed by seven days of enhanced self-management protocols, the CECC said.

The CECC first introduced quarantine restrictions for flight crews in March 2020 to prevent the potential spread of COVID-19.

The rules were tightened in late December after an EVA Airways pilot infected two of his colleagues and a friend of his in Taiwan, in what was the country's first confirmed domestic transmission case in over 250 days at the time.

The CECC decided to relax quarantine requirements in March, and again in mid-April, saying at the time that domestic carriers and flight crew members had been closely observing disease prevention measures while on duty.

In late April, however, a cluster infection involving China Airlines and an airport hotel in Taoyuan broke out and eventually grew to 36 cases, and may have also triggered the major spike in cases that started in mid-May.

Many blamed the April cluster on the short quarantine that flight crew members were entitled to at the time.

In tightening the restrictions, the CECC also addressed long-haul flight crew who received their first COVID-19 vaccine dose two weeks prior to their assignment.

They will still be subject to the previously required three-day quarantine and 11 days of regular self-management protocols that entail wearing a mask at all times outside their homes and checking their temperatures twice per day.

However, they will receive a PCR test on their final day in quarantine and two rapid COVID-19 tests in the following days, according to the CECC.

Quarantine rules for this group will be tightened starting July 1, when they will be required to be quarantined for five days and then follow enhanced self-health management protocols for nine days.

The quarantine requirements for fully vaccinated long-haul flight crew members remain unchanged -- seven days of following self-health management protocols and a PCR test -- but the CECC said Monday it has decided to test vaccinated crew members for COVID-19 antibodies every three months.

Rules for flight crew on one-day return flights also remain the same -- 14 days following self-health management protocols for the unvaccinated and no rules for the vaccinated.

Mandatory PCR tests will be required for these flight crews every two weeks, however.

As of Monday, 83 percent of pilots and 57 percent of flight attendants at domestic carriers had received their first COVID-19 vaccine shot, according to Deputy Interior Minister Chen Tsung-yen (陳宗彥), who is also deputy head of the CECC.

They will begin to receive their second COVID-19 vaccine shots later this month, Chen said.