It was claimed previously to be 48 hours. That always seemed extremely suspicious to me as the shot is permanently altering your immune system. What would make it suddenly stop producing spike protein?
And finally this study came out:
https://www.cell.com/cell/fulltext/S0092-8674(22)00076-9
They found the spike protein persists in the body for at least 16 days post-vaccination and the antigen can be found for at least 60 days. That is longer than getting covid via infection.
I got my first shot in April 2021. What I found at the time was that manufacturers mostly did not provide that info, or when they did, it was vaguely given (usually described as "a couple weeks"). There are a multitude of potential reasons: They didn't know (unlikely), the PR people asked didn't know, it was different for different shot brands, it is probably variable person to person, and the most important one in my opinion, they were aware that it was a stupidly politicized issue and didn't feel that the specific info of "how long" would be useful to the community and un-useful to the vaccine skeptic community, and were very confident that an mRNA based solution would be 100% degraded "eventually" just because of how cells work.
When biostats does a project, we have to stratify our patient comparison groups on age, gender, and sometimes even 'approximate cash' as all of these change risks and outcomes. The outcome for healthy < 40 year olds is vastly different than the outcome for healthy > 60 year olds.
The question is not 'is the vaccine better than the infection' - its 'for healthy women in child bearing age, is the impact of a vaccine better than the impact of an infection on their fertility.'
I am guessing that you don't have quite the eye roll for this more nuanced question.