The BA.4 and BA.5 sub-variants of Covid-19 are more severe than other sub-variants of the Omicron strain, and less affected by antibodies, according to the Department of Medical Sciences.
Director-general Supakit Sirilak said in his weekly update on the BA.4 and BA.5 situation on Monday that BA.4 and BA.5 cases had grown steadily in Bangkok over the past four weeks, from 12% to 50%, 68% and 72% of examined cases.
"Most cases in Bangkok were BA.4 and BA.5 infections, like imported cases," Dr Supakit said.
He said, BA.4 and BA.5 infections also gradually increased in other provinces, from 6% to 17% and 34% on a weekly basis.
"BA.4 and BA.5 infections started to surpass BA.1 and BA.2 slowly... BA.4 and BA.5 were more widespread in Bangkok than in other provinces, but naturally such a situation begins in Bangkok and will gradually expand to other areas," Dr Supakit said.
Regarding the severity of BA.4 and BA.5, he said 77% of patients with severe lung inflammation and fatalities in Bangkok had the two sub-variants, while 23% of them had the BA.2 sub-variant of Covid-19's Omicron strain.
In other provinces, BA.4 and BA.5 were found in 47% of people with serious lung inflammation and those who died. More than 33% of patients with mild symptoms were diagnosed with BA.4 and BA.5.
"So, data from Bangkok and other provinces initially indicate that BA.4 and BA.5 sub-variants are more severe than BA.2," Dr Supakit said.
Globally, BA.5 was confirmed in 52% of Covid-19 cases between June 26 and July 6, up from 37% in the June 19-25 period. BA.4 was in 12% up from 11%, Dr Supakit said, citing data from the World Health Organisation.
"This shows that BA.5 is more transmissible than BA.4," he said.
However, WHO had not concluded BA.4 and BA.5 were significantly more severe that other sub-variants, he said.
So far, worldwide data showed that antibodies were less effective at protecting against the two sub-variants, Dr Supakit said.
"This means that those who earlier caught BA.1 or BA.2 sub-variants can again be infected with BA.4 and BA.5 sub-variants," he said.
People should continue to wear face masks, wash their hands frequently and avoid crowded places, so that hospital beds would not be fully occupied in the event that BA.4 and BA.5 were both highly transmissible and really more severe, Dr Supakit said.