A big change is that from July 11 2016 when you have a yellow fever vaccination the certificate will now say that the vaccine is valid for the lifetime of the person vaccinated instead of 10 years as it was previously. This follows a decision from WHO because the protection from the vaccine is longer than 10 years for most people. The American CDC however warns that if someone is going to a high yellow fever risk region, were pregnant when they were first vaccinated or HIV positive a second dose may be indicated. It also remains to be seen if the border officials of all countries accept the new duration of protection. If travelling with an expired certificate is should not be altered in any way but should be considered adequate.