For many countries specific vaccinations are necessary to protect you against (tropical) diseases. Different regulations apply per country and sometimes per region within the country. The National Health Service’s website provides an up-to-date overview of the vaccinations required in each country:
If you are travelling for over than three months, it is wise to make an appointment to discuss your travel plan with an expert. Do this well (a few months) in advance! As the vaccinations often protect you for a long time, it is better to go too early than too late. In some cases, such as the anti-rabies vaccination, you will need a vaccination three times every few weeks. So if you think about this just before departure, you’re too late! And in the popular holiday months they don’t always have space for you at the vaccination centres.
Vaccinations are not cheap. Depending on the type of health insurance you have, you may be (partially) reimbursed. On the website of NHS, you can check which travel vaccines are free. Don’t forget to bring your vaccination booklet with you on your trip! Put it in your hand luggage, because sometimes it is necessary to obtain a visa.