Rwanda, Kenya, and D.R.Congo require that a traveller have a yellow fever vaccination before they enter the country but Uganda and Tanzania are not quite strict unless you have been exposed to yellow fever or are coming from a part of the world known to have yellow.
It’s important to note that since all these countries are in the tropics, chances are high you may get malaria from mosquitoes bites so it would be wise for you to take malaria prophylaxis medication to boost your immunity against malaria or use repellents to minimize mosquito bites.