What about simple vitamin D, and the fact that people in places like Africa aren't as sedentary as us the majority of Westerners? The lympatic system doesn't have a pump per se, so it requires activity to facilitate movement throughout the the body. At least that is my understanding.
No doubt vitamin d is critical. Also, Malarial type parasitic illnesses are extremely common, so everyone has reserves of the “Sunday Pill” (Hydroxychloroquine)