BANGKOK, Thailand – A leading Thai virologist has raised concerns over a growing outbreak of Hepatitis A in eastern Thailand, warning that younger populations may be particularly vulnerable due to low immunity.
Dr. Yong Poovorawan, a senior expert at the Faculty of Medicine, Chulalongkorn University, said in a recent Facebook post that 2026 is seeing a relatively high level of Hepatitis A transmission, with cases already emerging earlier than expected.
Younger generations at higher risk
He explained that while Hepatitis A spreads easily through contaminated food and water, immunity levels vary significantly by age group:
Most people over 60 years old already have immunity from natural infection in the past
Around half of those aged 40–50 have some immunity
The majority of people under 40 lack immunity, unless vaccinated
Improved sanitation in recent decades has reduced early-life exposure, meaning younger generations have not developed natural immunity and are therefore more at risk.
“Hepatitis A infection usually occurs only once in a lifetime, after which immunity is long-lasting,” he noted.
Spread linked to hygiene and crowded environments
The virus is transmitted via the fecal-oral route, often through contaminated food, water, or surfaces. While outbreaks are commonly blamed on drinking water contamination, Prof. Yong said the true source is often harder to trace.
He suggested that clusters may originate in large workplaces, particularly where migrant labor is present, allowing the virus to spread in close-contact environments before being detected.
He emphasized that strict hygiene—especially handwashing after using the toilet—is critical, particularly for workers in food production and food service sectors. Vaccination for these groups is also strongly recommended to reduce transmission risks.
Raw and undercooked seafood a key concern
Another major risk factor highlighted is seafood consumption.
The virus can survive in seawater, and shellfish such as oysters and blood cockles can accumulate the virus while feeding. If eaten raw or only lightly cooked, they may carry infection.
To effectively kill the virus, food must be heated to at least 85°C, he said. Dishes that are only briefly blanched or served raw may not reach sufficient internal temperatures.
He pointed to past large-scale outbreaks, including one in Shanghai decades ago that affected hundreds of thousands of people, as an example of how contaminated seafood can trigger widespread infection.
Early outbreak raises concern ahead of rainy season
Hepatitis A outbreaks in Thailand typically occur at the start of the rainy season. However, this year’s early spread during the hot season is raising concerns that case numbers could rise significantly in the coming months.
