I have just been reading random RTW posts. Can't see much reference to vaccinations for RTW, so here goes.
Most vaccinations are only 'recommended', however a notable exception is Yellow Fever. Some vaccinations you may opt for require a series of jabs for example, Hepatitis B is a series of 3 injections over 4 weeks. For this reason the immunisation timeline needs to be addressed early on.
There are vaccination 'recommendations' for all countries. A really useful website providing advice for people travelling abroad from the UK, Fit for Travel, comes to you courtesy of the venerable NHS. Just select your destination from either the drop list on the landing page or the interactive map and frighten the life out of yourself.
For those heading to South America, specifically Brazil, you will require a Yellow Fever Vaccination and a Certificate to prove you have been immunised (essential if say, you ever desire to return to the UK and most other countries on the planet). Check for your nearest UK Yellow Fever Vaccination centre at: Yellow Fever Vaccination Centre.
Some vaccinations are free, others are not. Some vaccination prices for August 2008: Yellow Fever £45, Rabies £126 (series of 3). Check with your local GP.
A word about Rabies, if you develop rabies, death is almost 100% certain.
Something/s to think about in the planning stages.
Then there's the malaria tablets.....