Thailand has recorded 49 new cases of the two new Omicron subvariants -- BA.4 and BA.5 -- which are considered more contagious and can potentially bypass immunity, according to the Centre for Medical Genomics of Ramathibodi Hospital.
Wasun Chantratita, who heads the centre, said 26 cases of BA.5, 23 cases of BA.4 and 18 cases of BA.2.12.1 have been detected in the kingdom since April. He cited data from Gisaid, the global data science initiative, to back up his remarks.
Dr Wasun said the figure was based on random tests so the true number of infections could be considerably higher. The patients were admitted to hospital and their condition described as manageable.
"Omicron is not the last variant of Covid-19," he said.
"Despite the easing of protective measures, people must not let their guard down and should keep wearing face masks, particularly in high-density areas, as well as making sure they get vaccinated."
He said most of the patients infected with the subvariants had come from overseas.
No cases of BA.5 and BA.4 have been detected in Bangkok or its adjacent provinces, Dr Wasun said.
Over the past two months, Gisaid reported that BA.2 accounted for 44% of the Omicron subvariants detected in Thailand. This was followed by BA.2.9 (26%), BA.2.10 (7%), BA.2.3 (5%), BA.2.10.1 (4%), BA.2.27 (3%), and BA.5, BA.4 and BA.2.12.1 (1% each).
BA.5 and BA.4 have also shown up in South Africa and many European countries.
The genome sequencing of BA.5 was found to have mutated from the original Wuhan strain by almost 90 strains, while BA.4 showed 80 such changes in its code.
The findings indicated these subvariants may be able to bypass immunity leading to high rates of transmission.
Cases of infection by one of the two have jumped 80% at hospitals in Portugal, and by 50% in the United Kingdom, Austria, Netherlands, France and other parts of Europe.
However, the World Health Organisation (WHO) has not yet raised the alert level against either subvariant, Dr Wasun said.
Meanwhile, Sorawit Thanito, director-general of the Department of Livestock Development, confirmed that a veterinarian in Songkhla had been diagnosed with Covid-19 last year after being sneezed on by an infected cat, which contracted the disease from its owners.
The research was carried out by the Prince of Songkla University's Department of Health Science and Medical Research.
Mr Sorawit said genome sequencing had confirmed the link in the infections between the vet, the cat and its owner.
The finding suggests the virus is indeed transmissible from animals to humans, although it is much harder to do so than from person to person.
Furthermore, some variants can cause fever-like diseases in humans and other forms of illness among cows, buffaloes, camels, bats and other mammals.
The investigation found that most pets appeared to contract the virus through close contact with their infected owners.
The department was monitoring the condition of pets that travelled with their owners from foreign shores to see whether they were at risk of getting infected, Mr Sorawit said.