Hepatitis A Outbreak Warning Issued in Eastern Thailand: Under-40s at High Risk, Health Officials Urge Vigilance

Thai health officials have issued urgent warnings about a significant hepatitis A outbreak spreading rapidly across central and eastern regions of Thailand, with cases doubling compared to the same period last year.

The Ministry of Public Health reported that hepatitis A cases have doubled in the summer of 2026, particularly concentrated in Bangkok, Chonburi, Rayong, and Chanthaburi. Authorities attribute the surge to contaminated ice and drinking water, noting that increased demand during hot weather raises transmission risks when production or transportation hygiene is inadequate.

Vulnerable Population Identified

Medical experts, including prominent virologist Yong Poovorawan from Chulalongkorn University’s Centre of Excellence in Clinical Virology, have highlighted that individuals under 40 years old in Thailand are especially vulnerable due to lower rates of natural exposure and vaccination in recent decades. Yong stated that most Thais under the age of 40 currently have no immunity against the virus unless vaccinated, while approximately 50% of those aged 40-50 are believed to have immunity, and most people over 60 have immunity from past natural infection.

Transmission and Symptoms

Hepatitis A is caused by a virus transmitted through the fecal-oral route, often via contaminated food or drinking water. The virus is highly resistant to environmental conditions and can survive in unclean ice or undercooked food. Key symptoms requiring immediate medical attention include mild fever, jaundice, and dark urine.

Preventive Measures Advised

Health authorities emphasize that preventive measures remain the most effective strategy against outbreaks. The Department of Disease Control continues to promote the hygiene guideline: “cook it, boil it, peel it, or forget it.” Officials urge regular handwashing with soap, especially after using the bathroom and before handling food, and advise vigilance regarding food and water hygiene during the rainy season when cases are expected to rise further.

Immunity and Vaccination Context

Although hepatitis A has multiple genotypes, it has only one serotype, meaning infection typically confers lifelong immunity. Yong explained that food and drinking-water hygiene has improved over time, reducing natural exposure for younger generations who must now rely on vaccination for protection. In contrast, older populations who grew up in eras with less sanitary water practices—such as sharing dippers—are more likely to have acquired immunity through past infection.

Official Response

The government has reiterated its warning for the public to remain vigilant, with Deputy Spokesperson for the Prime Minister’s Office Lalida Pertwiwatthana stating concern over cluster outbreaks due to the disease’s ease of transmission through contaminated food and water. Health officials continue to monitor the situation closely, particularly in tourist and economic zones where transmission risks are heightened.