You can get a mixture of the J&J and Pfizer vaccines against COVID-19 in South Africa. You just have to be fully vaccinated with one, then ask for the other as a booster. However, if you are 50 and over, your last booster shot (e.g. your 3rd booster if you started with J&J, and your 2nd booster if you started with Pfizer) must only be Pfizer.