Blood and body fluids, not food
Hepatitis B is a very different proposition from hepatitis A despite the shared name. It is not in the water supply. It travels in blood and body fluids - a medical procedure with reused equipment, a transfusion in a country with thin screening, a tattoo needle, unprotected sex, sometimes a shared razor.
It is also far more durable than hepatitis A. The virus survives outside the body for days, infects at very small doses, and in a proportion of adults becomes a lifelong infection carrying a real risk of cirrhosis and liver cancer decades later. That long tail is why the vaccine is worth having even though the chance of exposure on any single holiday is small.
Three schedules, depending on your flight date
The standard course is three doses over six months and gives the most reliable response. An accelerated course - day nought, one month, two months - works well and is what most travellers end up on.
When the trip is weeks away rather than months, a very rapid schedule of day nought, day seven and day twenty-one can be used for adults, with a fourth dose a year later to lock it in. It is not the first choice clinically, but it is enormously better than going unvaccinated, and it is the reason to walk in rather than write the vaccine off because you left it late.
Who should have a blood test afterwards
Most travellers do not need their immunity checked. Healthcare and laboratory workers generally do, because their employer requires documented antibody levels rather than a completed course.
We do not run that blood test here. If you need one we will say so plainly and tell you to arrange it through your GP or occupational health rather than sending you away thinking it is covered.