As for going to Kenya, I suggest you go. Although customs officers do not necessarily check the yellow book when entering Kenya, the entry health and quarantine department has such regulations. If you happen to be checked when you enter the country on the same day, it will be very troublesome, because the customs has no place to give you an on-site injection (your immune function usually takes effect after 3 days of injection), so you will be banned from entering Kenya.
At present, there is a valid period of 10 years after vaccination, which means that if you go to a country that needs yellow books in the future, 10 years does not need to be vaccinated again.