I will be traveling to South Africa and Mozambique from the United States. Is a yellow fever immunization necessary?
Here's some information which will help, but it sounds like it's a good idea to get one to save complications.
In September 2007, the Mozambican Interior and Health Ministries decreed that all travelers entering Mozambique who had previously visited a country where yellow fever is present must present a valid certification of vaccination against yellow fever. We recommend all travelers be vaccinated to avoid complications at the border. Any passenger who cannot present such a certificate at the port of entry will be vaccinated at a cost of $50 US dollars or the equivalent in metical. Additionally, all travelers entering Mozambique must carry their yellow vaccination book about 7 years ago