At least one foreign national was detected carrying an Omicron sub-variant that could cause severe infections, according to the Department of Medical Sciences.

Supakit Sirilak of the DoMS said Omicron has become the dominant coronavirus strain in Thailand, with the BA.2 sub-variant attributed to 97.6% of infections in the country.

The World Health Organization (WHO) warned of three infectious Omicron sub-variants -- BA.4, BA.5 and BA.2.12.1, he said.

Omicron sub-variants, BA.4 and BA.5, were first discovered in South Africa in January and February, he said, while BA.2.12.1 was discovered in the United States in February.

However, sub-variants BA.4 and BA.5 have since been found spreading in many countries, including Botswana, South Africa, Germany and Denmark, while BA.2.12.1 has been detected in Canada and India, he said.

In Thailand, testing confirmed that a Brazilian national has BA.5, while two others, an Indian and a Canadian, have BA.2.12.

As of now, sub-variants BA.2.12.1 and BA.4 have not yet been discovered in Thailand, Dr Supakit said.

Dr Supakit noted that those infected with BA.1 have weak immunity against BA.4 and BA.5 sub-variants. However, fully vaccinated people have stronger immunity against the two sub-variants, he said.