Three new confirmed Covid-19 cases were reported on Friday morning - two Thais infected in Myanmar who sneaked back across the border, and a woman who travelled on a plane to Bangkok.
The 51-year-old woman was from Sing Buri province, said Dr Sophon Iamsirithaworn, of the Disease Control Department. She flew from the northernmost province of Chiang Rai to Bangkok on the same flight as two confirmed cases who had returned from working in Tachilek without passing through immigration or quarantine.
He said health officials were questioning the woman to find out where she most likely caught the virus.
The woman told officials she had not visited Myanmar. If that was verified, she would be considered as another case of local infection, Dr Sophon said.
The two other new cases were returnees from Tachilek and officials were contacting people who had been in close contact with them. He expected more Covid-19 infections would be found and confirmed to be linked to the latest returnees.
According to media reports, the Sing Buri woman visited Chiang Rai from Nov 25 to 28 on business.
On Nov 28, she took Nok Air flight DD8717 from Chiang Rai airport to Bangkok's Don Mueang. Two women who have since been confirmed as cases coming from Tachilek were on the same flight. One of them lives in Bangkok and the other in Phichit province.
From Bangkok, the Sing Buri woman returned to her factory in Ang Thong province, and later went to her home in adjacent Sing Buri.
On Monday she received influenza vaccine at In Buri Hospital. On Wednesday she had body pains and initially thought it was a reaction to the flu jab.
On Thursday she learned about the Covid-19 cases on the same flight, and sought a Covid-19 test at Bang Rachan Hospital. Her test result was known on Friday morning. It was positive.
