The Ministry of Health last week clarified that while the new coronavirus strain originating in the U.K. has a higher basic reproduction number than previous strains and faster onset time, its incubation period remains two weeks.

The quarantine had been increased to 21 days instead of the usual 14 following the outbreak in northern Vietnam at the end of January.

Some 19,000 people are now in quarantine.

While the outbreaks in Hai Duong and Quang Ninh provinces are gradually coming under control, authorities are struggling with a new outbreak at Tan Son Nhat International Airport in HCMC with which 30 cases of community transmissions have been linked.

The source of the airport cluster has not been found.

The outbreak in Vietnam’s biggest city comes just a few days before the Lunar New Year, or Tet, the country’s most important holiday which sees people flock back home to celebrate.

Vietnam has had 470 cases of community infection since January 28.