How old the last vaccine can be?

I'm from a country that started the vaccination process very early on. So I got a 4th vaccine dose on May 2022. I'm going to be on Japan on February 2023. I will need another booster dose or I will be ok with four doses even if it will be about 9 months since my last one when I arrive on Japan? Anyone has info about this? In all of the official pages says "3 doses" but doesn't say anything about the dates of those doses.

From memory, information pertaining only to the first three vaccination dates and types were required when filling the forms online. My vac certificate shows 4 but I�fve had 5 (the most recent is a bivalent vac).

I too wandered about the whole point of requiring 3 shots irrespective of when it�fs given & the efficacy is diminished.
Perhaps, you should speak with your GP regarding a bivalent booster as added protection?

Japan does not care when you got any of the shots (besides the fact that the vaccination certificate needs to state the dates of all shots). As long as you have at least three of them.