when the wife & i had our jabs we were given a badge type sticker & also a card with the details ,date names health No etc so that is our proof i suppose. many years ago with being a seaman i had to have a W.H.O book that stated all immunisation jabs that one has had. that was usually ok until a trip to west africa or western south america where a ship may do up to 30 ports along each coast & the local doctor would not recognise any of the previous doctors jabs & we had to have them again . did 14 ports alone in Chile & got 8 yellow fever needles. even returned to Valparaiso on our way up the coast & was given another jab & the same clinic had given us all the previous one. merchant ships at that time carried 40 - 60 crew., so a good earner for the local quacks & i doubt very much if the contents of the syringes had the real mcoy in them.