We were lining up at the Kenyan border post, ready to enter Tanzania. Unfortunately, my friend Lai and I were stopped and queried because we failed to produce our yellow fever vaccination certificates... which were actually in our checked baggage!
The certificate is a yellow 16-page booklet that has been issued to travellers since 1969 by the World Health Organisation (WHO). Each yellow fever vaccine is valid for 10 years. The certificate guarantees a traveller passage into the 43 countries in the African continent, as well as countries in South and Central America.