Thailand's six new imported cases of Covid includes three Thai men who were previously infected but had been certified virus-free before flying from Singapore.
The Centre for Covid-19 Situation Administration (CCSA) said on Sunday the three men -- aged 43, 53 and 56 -- tested postitive for the virus after arriving on Friday.
An official at the CCSA call centre said they had contracted the virus in Singapore, but then made a full recovery. They applied for and received certificates of good health from the Thai embassy before boarding the flight, as required for every person flying into Thailand.
The men were tested again upon arrival -- and diagnosed with Covid-19.
It was not immediately clear how the course of events could have taken place. The final Singapore tests or the tests on arrival in Thailand could have delivered incorrect results. Alternatively, the men caught the disease, recovered and then caught it again. That would imply they had no immunity to the disease even after contracting it, which could make any vaccine ineffective.
The CCSA said that three other imported cases were recorded on Sunday.
Two Thai nationals, a 46-year-old maid and a woman aged 83, returned from the United States on Monday.
The sixth case was a 46-year-old Frenchman who arrived from the United Kingdom.
He was a language teacher at a private school in the country.
The new infections, all asymptomatic, took the total tally of infections in the country to 3,444, while no new fatalities were reported.
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