BA.4 and BA.5 will soon be the dominant sub-variants of Covid-19 in Thailand, but have so far not been shown to cause severe illness, according to the Department of Medical Sciences.
Director-general Supakit Sirilak said on Monday that BA.4 and BA.5 caused more than 50% of all new Covid-19 cases over the past week.
"The sub-variants will gradually replace other sub-variants, like the Omicron variant itself did to Delta previously," he said.
There was not enough information to make a conclusion about the severity of Omicron's BA.4 and BA.5 sub-variants, but health officials assumed that they were slightly more transmissible, he said.
Dr Supakit said that last week the Omicron variant accounted for 100% of new local and imported cases, as it did worldwide.
BA.1 formed one percent of new Covid-19 cases, with the rest roughly equally split between BA.2 and BA.4/BA.5.
About 1,000 people had been confirmed to have BA.4 and BA.5 sub-variants in Thailand so far. The most cases were in Bangkok.
Dr Supakit said BA.4 and BA.5 cases had not shown severe symptoms to date.
"No need for panic about the sub-variants. Although there were more admissions to hospital, we have yet to find out if the increase resulted from BA.4 and BA.5 or from more infections, like when Omicron had just erupted," he said.
Dr Supakit said that personal protection was still necessary, especially when in crowded areas. He referred to the use of face masks and booster shots of vaccine to stimulate antibody production.