Hepatitis B Vaccine: Who Needs It, How Many Doses, and Is It Too Late If You Are Already Exposed?

Clinically reviewed by Dr. Pipat Finn, M.D., Senior Doctor, Doctor Pattaya. Last reviewed: August 2026

You have been in Pattaya for a few days. Maybe something happened last night and you are now Googling hepatitis B at 2am. Maybe you are an expat who got vaccinated years ago and genuinely cannot remember if you finished the course. Maybe you are settling in for a longer stay and want to get sorted before anything happens. All three of those people walk into Doctor Pattaya regularly, and the questions are almost always the same.

Thailand carries a moderate-to-high hepatitis B burden. The virus circulates here at levels you would not see in most Western countries. The good news is that the vaccine works well, the schedules are flexible, and even if you think you may have already been exposed, there are steps we can take right now.

How Hepatitis B Spreads and Why Pattaya Raises Your Risk

Hepatitis B spreads through blood and body fluids. Unprotected sex is the most common route in adults. Shared needles, unsterile tattoo or piercing equipment, and dental or medical procedures done with inadequately cleaned tools can all transmit it.

Pattaya has specific risks that a generic travel health page will not mention. The nightlife is obvious. But there is also a busy tattoo and piercing scene, a popular dental tourism market, and a steady stream of travellers making quick decisions about procedures they would never rush at home. Knowing your actual risk is what helps you make the right call.

Hepatitis B can also pass from mother to baby at birth. If you are pregnant or planning to be, vaccination matters a great deal.

Who Actually Needs the Hepatitis B Vaccine

If you were not vaccinated as a child and have not completed the full adult series, you need it. That applies to most tourists who grew up in countries where the vaccine was introduced later or not offered at all.

Long-term expats in Pattaya who cannot confirm they finished the series should get a blood test first. We check your antibody level and can tell you in the same visit whether you are already protected or need doses.

People with higher baseline risk should be especially motivated. That includes anyone in healthcare, anyone with multiple sexual partners, people who use injectable medications, and anyone planning tattoos or dental work during their time in Thailand.

How Many Doses You Need and What the Schedule Options Are

The standard course is three doses: one now, one at one month, and the third at six months. This gives strong, long-lasting immunity.

For travellers already in Pattaya who need faster coverage, there is an accelerated four-dose schedule using Engerix-B or Twinrix, the combination hepatitis A and B vaccine. Doses go at months zero, one, and two, with a booster at twelve months. You get meaningful protection within weeks. The twelve-month booster is required to lock in long-term immunity, and you can get that wherever you are at the time.

There is also a two-dose option called Heplisav-B, given one month apart with no booster required. It is not available everywhere, but it is a genuine option for people who want the shortest complete course.

What to Do If You Missed a Dose or Started the Series Abroad

You do not need to restart the series, no matter how long it has been since your last dose. The hepatitis B vaccine picks up from where it stopped. The next dose should follow the minimum interval from your previous one.

A lot of travellers in Pattaya have had one or two doses somewhere else and are not sure what to do next. Walk in with your vaccine record if you have one. We will check the timing and give you the next dose on the spot.

Is It Too Late for the Hepatitis B Vaccine If You Are Already Exposed

This is the most urgent question, and timing is everything.

If you had unprotected sex, a needlestick, or any other high-risk exposure and you have never been vaccinated, treat this as a medical urgency. Post-exposure prophylaxis involves hepatitis B immune globulin, which provides immediate short-term protection, plus the first dose of the vaccine. Together they can prevent infection from taking hold. The window is 24 to 48 hours after exposure. After that, effectiveness drops significantly.

Do not wait until morning if this happened last night. Doctor Pattaya is open around the clock. Come in now.

If you have already had some doses of the vaccine and had a potential exposure, your situation is usually less urgent. A partially vaccinated person may already have some immunity. We can check with a quick blood test and guide the next steps from there. For a full picture of risk and testing options, our STD testing and treatment service covers hepatitis B alongside HIV, syphilis, gonorrhoea, chlamydia, and hepatitis C in a single confidential visit.

How to Know If the Hepatitis B Vaccine Has Worked

Most healthy people who complete the full course develop strong immunity. But some people, called non-responders, do not produce enough antibodies even after three doses.

This is more common in people over 40, people with diabetes or kidney disease, and heavy smokers. If you fall into any of these groups, a blood test after completing the series is worth doing rather than assuming the vaccine worked. We offer that antibody titer test at Doctor Pattaya. If your level is low, we can give a booster dose in the same visit and recheck afterward.

Do You Need a Booster If You Were Vaccinated Years Ago

For most healthy adults, the hepatitis B vaccine provides protection that lasts decades and likely a lifetime. Routine boosters are not recommended for people who completed the series and had a good antibody response.

If you are an expat who finished your series years ago and has never had a titer check, or if you have a health condition that affects your immune system, a quick blood test is worth doing. It takes a few minutes and gives you a clear answer. If your level is fine, you need nothing further. If it has dropped, a single booster dose is usually enough.

Getting the Hepatitis B Vaccine at Doctor Pattaya

We are a 24/7 walk-in clinic in South Pattaya, and hepatitis B vaccination is one of the most common things we handle. No appointment needed. We stock Engerix-B and Twinrix, offer all main schedule options, and can run an antibody titer test in the same visit to check existing immunity before we start.

If you need a vaccine and an STD screen after a potential exposure, we can do both in one appointment. That combination is genuinely common here and nothing to be awkward about. We provide an official vaccination certificate after each dose, which some employers and visa applications require.

We also do hotel visits across Pattaya, Jomtien, Naklua, and Pratumnak if you would rather not travel. Call us and we will come to you.

Vaccine Side Effects and What Is Normal

The hepatitis B vaccine has a strong safety record. A sore arm for a day or two is the most common reaction. Some people notice mild fatigue or a low-grade temperature for 24 hours.

Serious reactions are rare. If you develop hives, swelling in the face or throat, or difficulty breathing after a dose, come straight in for assessment.

I had unprotected sex in Pattaya last night and have never been vaccinated against hepatitis B. What should I do?

Come in now. Post-exposure prophylaxis works best within 24 to 48 hours and involves an injection of hepatitis B immune globulin for immediate short-term protection plus the first dose of the vaccine. Doctor Pattaya is open 24/7 and can assess and start treatment on a walk-in basis. We can also run a full STD screen in the same visit.

How many doses of the hepatitis B vaccine do I need and how long does the course take?

The standard course is three doses over six months. If you are already in Pattaya and want faster coverage, an accelerated four-dose schedule gives meaningful protection within weeks, with a booster at twelve months. There is also a two-dose schedule one month apart for the shortest complete course. All options are available at Doctor Pattaya.

I was vaccinated against hepatitis B as a child. Am I still protected?

Probably yes. For most healthy people, the vaccine provides long-lasting and likely lifelong protection. Protection can be lower in people vaccinated later in life, those with diabetes or kidney disease, or those who may not have responded well originally. A simple blood test tells you exactly where you stand, and we can give a booster on the same visit if needed.

I have only had one dose of the hepatitis B vaccine. Do I need to restart?

No. You never need to restart the hepatitis B series regardless of how long it has been since your last dose. Walk in with your vaccine record if you have it and we will check the timing and give you the next dose on the spot.

Can I get the hepatitis B vaccine and an STD test at the same appointment?

Yes, and it is a very common combination at Doctor Pattaya. We offer hepatitis B vaccination alongside full STD testing including hepatitis B surface antigen, hepatitis C, HIV, syphilis, gonorrhoea, and chlamydia, all in one confidential appointment. No advance booking required.

What is the difference between Engerix-B and Twinrix?

Engerix-B covers hepatitis B only. Twinrix is a combination vaccine covering both hepatitis A and hepatitis B in a single injection. For most travellers in Thailand, Twinrix is worth considering since hepatitis A is also a real risk here, particularly from food and water. We can talk through which suits your situation when you come in.