While the BA.1 subvariant was still behind most new infections in Bangkok, BA.2 cases are catching up, Yong said.
Also known as the "stealth variant" because it can evade detection in PCR tests, the BA.2 subvariant now accounts for about 18.5 per cent of new Covid-19 infections in Thailand, according to the Public Health Ministry.
Yong said that while BA.2 does not cause more severe symptoms than BA.1, it spreads faster and will eventually cause more infections.
Meanwhile, recent lab experiments in Japan show BA.2 also blunts immunity created by vaccines. However, a booster shot cuts the chances of illness after BA.2 infection by about 74 per cent.
On Friday, Thailand logged 18,885 new Covid-19 infections over the previous 24 hours, 224 of whom have arrived in Thailand from abroad. The death toll increased by 29, while 10,946 patients recovered and left hospitals