All countries have occasional outbreaks of dangerous illnesses or diseases.
Additionally, to keep people from spreading diseases to people in other places, some countries make you prove that you have been immunized against certain diseases if you have been to a place where there has been a recent outbreak. The best way to prove this is by carrying an International Certificate of Vaccination Card which is a record of all your vaccinations. Each time we go to get a vaccination, it will be recorded on our cards by the person who gives us the vaccination. They have information about what diseases mosquitoes carry as we are certain to encounter a lot of those annoying critters.