Hepatitis A: The Food-and-Water Liver Infection a Vaccine Prevents

Of the hepatitis viruses, A is the one most tied to everyday life abroad: it spreads through food and water, not blood or sex, which puts it squarely in the path of anyone eating out in a new country. It's also the one with the most reassuring story — it doesn't become a chronic infection, and a highly effective vaccine prevents it. The catch, especially in Thailand, is that fewer people are naturally immune than they used to be. This is a plain-language guide to what hepatitis A is, what the blood tests mean, and why the real answer is usually a vaccine rather than a test. It's general education, not a diagnosis.

What is hepatitis A?

Hepatitis A is a liver infection caused by the hepatitis A virus (HAV). It spreads by the faecal–oral route — swallowing tiny, invisible amounts of the virus from contaminated food or water, or through close contact with someone infected ². That route is why it's a classic travel and food-hygiene infection rather than a blood-borne one.

The single most important thing to know is how it differs from its better-known cousins. Hepatitis A is almost always acute and self-limiting, and it does NOT become chronic — unlike hepatitis B and C, which can quietly persist in the liver for decades ¹. Most people with hepatitis A recover completely, with no lasting liver damage, although the illness itself — fatigue, nausea, poor appetite, jaundice — can drag on for weeks to a couple of months.

Who gets seriously ill?

For most healthy adults and children, hepatitis A is unpleasant but not dangerous. Young children under six often have no noticeable symptoms at all ². But it isn't trivial for everyone: severe, even life-threatening liver failure is rare but real, and the risk rises with age and with existing liver disease ¹. That's why the people who most need protection are older travellers and anyone whose liver is already under strain.

The two blood tests, and the different questions they answer

This is where people get confused, because "a hepatitis A test" is really two different tests answering two different questions ³:

• Anti-HAV IgM answers "Do I have it now?" — it signals a current or recent infection, detectable from shortly before symptoms begin until about six months afterward.
• Anti-HAV IgG (or "total" anti-HAV) answers "Am I immune?" — it reflects past infection or vaccination, and it lasts long-term.

A practical point: the IgM test is for diagnosing someone who's actually ill, not for screening healthy travellers ³. Because false positives and lingering results happen, testing is done when acute hepatitis A is genuinely suspected — not ticked onto a routine panel "just in case."

The real answer: vaccination

For anyone well, the useful action isn't a test — it's the vaccine, which is excellent. Over 90% of people develop protective antibody levels within a month of the first dose, and protection has been documented to last at least 20 years after the full two-dose series, with no routine booster needed ⁴. Health authorities recommend it for travellers to countries where hepatitis A is common, which includes much of Southeast Asia ⁴.

If you've already been exposed, there's a window to act: the vaccine (sometimes with immune globulin) works as post-exposure prevention if given within about two weeks ⁴.

Why this matters specifically in Thailand

There's a twist that catches long-term expats and visitors off guard. As sanitation in Thailand improved, far fewer children grew up catching hepatitis A naturally — so the country shifted from high to very low endemicity, leaving a growing pool of susceptible adults. The numbers are striking: the age at which half the population is immune rose from about 4.5 years in the early 1970s to roughly 42 years by 2014, and recent surveys found only around 7–11% of Thais aged 3–20 were immune ⁵. Hepatitis A isn't in Thailand's routine childhood vaccination schedule, so most young Thais — and most unvaccinated visitors — simply aren't protected. Lower circulation is good news, but it means more non-immune people who could be caught out by an outbreak.

What we see at the clinic

The hepatitis A conversation in Pattaya usually starts one of two ways: someone unwell with jaundice and nausea who needs an actual diagnosis, or — far more often — a well expat or traveller asking whether they're protected. For the first, the right test is anti-HAV IgM, read in context. For the second, the honest and useful answer is almost always about the vaccine: are you covered, and if you don't know, a simple immunity (IgG) check or just getting vaccinated settles it. We don't run hepatitis A antibodies as a reflex on every panel — there's no point screening healthy people with the IgM test — but we do think it's one of the more worthwhile vaccines for anyone living in or travelling around this region. As always, diagnosis and treatment of actual illness is a doctor's job, not something to read off a single result.

Common questions

Is hepatitis A the dangerous one that stays in your liver? No — that's the common mix-up. Hepatitis A is acute and self-limiting and does not become chronic; it's hepatitis B and C that can persist for years ¹. Most people recover from hepatitis A completely.

Should I get tested for hepatitis A? If you're ill with possible hepatitis, yes — the IgM test helps diagnose it. If you're well, testing isn't a screen; the useful step is checking whether you're immune or simply getting vaccinated ³. The IgM test isn't meant for healthy-traveller screening.

How is it spread — do I need to worry about food here? It spreads through contaminated food and water, so food and water hygiene matters ². But the most reliable protection by far is the vaccine, which is why that's the standard advice for the region rather than relying on caution alone.

How good is the vaccine? Very. Over 90% of people are protected within a month of the first dose, and protection lasts at least 20 years after the full course ⁴. It's one of the more effective travel vaccines available.

I think I was exposed — is it too late? Maybe not. The vaccine, sometimes with immune globulin, can still prevent illness if given within roughly two weeks of exposure ⁴ — so it's worth seeing a doctor promptly rather than waiting for symptoms.

Key takeaway

Hepatitis A is the food-and-water hepatitis — spread by the faecal–oral route, and unlike hepatitis B and C it's acute and self-limiting, never chronic ¹. The blood tests answer two different questions — IgM for "do I have it now," IgG/total for "am I immune" — and the IgM test is for diagnosing illness, not screening the well ³. The genuinely useful takeaway is prevention: the vaccine is over 90% effective and lasts decades ⁴, and because most young Thais and unvaccinated visitors are no longer immune ⁵, it's one of the more worthwhile protections for living in or travelling around Pattaya. If in doubt about your status, ask a doctor about a quick immunity check or simply getting vaccinated.