The Delta Covid-19 variant has taken over the Alpha variant as the dominant strain in the country, accounting for 63% of infections, according to the Department of Medical Sciences.
Dr Supakit Sirilak, the department's chief, said about 63% of more than 3,000 cases analysed by the department are found to be the Delta strain, first detected in India, while 34% are the Alpha variant, first discovered in the UK. The rest are the Beta strain which is dominant in the deep South.
Eleven provinces -- Mae Hong Son, Kanchanaburi, Samut Songkhram, Chachoengsao, Trat, Surin, Chumphon, Nakhon Si Thammarat, Krabi, Phangnga, and Pattani -- reported their first Delta cases recently, raising the number of provinces where the variant was detected to 72.
He said the spread of the highly contagious variant is behind the surge in infections.
The Beta variant, which initially surfaced in South Africa, is dominant in Narathiwat but more cases are also being found in the surrounding provinces of Pattani, Yala, Songkhla and Phatthalung. Chumphon, a province further up in the South, has detected its first Beta variant case.
Dr Supakit said health authorities are investigating a case of Beta variant in the northeastern province of Bung Kan and keeping a close watch on the situation there after a Thai man who returned from Taiwan was found infected with the strain.
The patient tested negative in quarantine but was found infected after returning to Bung Kan. Three more close contacts were later confirmed as infected. More testing was under way.
He said three of Beta variant infections in Bangkok are linked to the patients in Narathiwat and if there are no new cases of this strain next week, the situation would be considered under control.
He added there were no new cases of of co-infections, after the department reported early last week that seven construction workers in Bangkok were suspected to have each been infected with a combination of the Alpha and Delta variants.