Thailand’s Covid-19 surge being driven by hidden infections: studies


While 60-70% of people in Thailand have been infected with Covid-19, more than half likely did not realise they had the disease, expert virologist Dr Yong Poovorawan said on Wednesday.

Writing on Facebook, Dr Yong cited two studies conducted by his Chulalongkorn University Centre of Excellence in Clinical Virology.

The first study of 190 children aged 5-6 found that the 10% infection rate during the Delta outbreak has now risen to 60-70% after Omicron. About 35% of these cases were asymptomatic and only discovered when blood tests came back positive.

The second study tested 700 people aged six months to 80 years old. Traces of previous or current Covid-19 infection were found in 60-70% of the test group. Yong said the infections were probably Omicron as subjects who caught Covid more than one year ago during the Delta wave would likely test negative. Some level of immunity via antibodies was detected in 95% of the test subjects.

Yong said it was impossible to determine what level of immunity is required to prevent Covid-19 symptoms because most people had been infected or vaccinated. Previous infection or vaccination was not a protection against catching Covid-19, he said. But repeat infections usually generated less severe symptoms.

Noting Thailand’s soaring infection rate as the cold season gets underway, Yong urged people to get a booster dose if it had been six months since their last vaccination or infection.

Thailand’s Covid-19 surge being driven by hidden infections: studies

He said all vaccine brands available offered similar protection against severe Covid symptoms but protection depended on the number of doses. He said immunity from vaccination decreased after the first few months. People should get a booster shot every six months, or every 4-5 months if they are in an at-risk group, he added.

Covid-19 hospitalisations have soared above 700 per day in recent weeks, with deaths rising above 10 per day. The surging infection rate has prompted the government to set up more vaccination sites in Bangkok and other Covid hotspots.

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