Vaccination
Before going to a different country, collect recommendations for vaccinations. You will get the best advice at a tropical health institute. Make an appointment early enough and carry your vaccination certificates. Their staff are able to give you exact and up-to-date recommendations specifically for the trip you are planning and your conditions. Some vaccinations may need several refreshment shots, some will interfere with others, so again: Make sure to start early.
You could also ask your doctor and contact people who are travelling there right now or have recently returned.
In order to enter certain countries, for example D.R. Congo, you must prove that you are vaccinated against yellow fever. It is necessary to get that shot and be able to produce a valid certificate. I got vaccinated against yellow fever in Germany, but I could have done it in Kenya, too. If you are doing a longer trip though several countries, find out what the exact conditions are and what suits you best.
Check with your insurance what they will pay for.
A note on malaria
There are a few medications on the market that serve as prophylaxis against malaria. They differ in possible side-effects, doses and prices. I tried one in two different cases and had very few problems. But I have also seen people getting malaria despite taking these pills. I have met people suffering heavily from the side effects. And I have had malaria myself several times and some relatives and friends got it.
Travel Responsibly. 