I agree with Johan. I travel quite extensively throughout Africa and never bother with meds. The only vaccine I have is Yellow Fever and that is because it is required at certain immigration points.

Maybe if I went trekking through a jungle area where malaria actually exists I would take precautions. But business traveling to African cities and visiting very popular tourist sites such as Kruger are about as safe as anything in America.

If you go down the wrong street at the wrong time in Nairobi or Chicago, you can get killed. If you are in the center during the business day, you will be fine in both cities. And while you are just as likely to get bitten by a mosquito in Chicago as you are in Nairobi, you are also just as likely to get Malaria in those cities.