There have at least been studies that have found mRNA after 15 (
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9313234/) and 28 days (
https://onlinelibrary.wiley.com/doi/10.1111/apm.13294) and other that show spike proteins months after vaccination.
not restricted to the injection site: https://www.thelancet.com/journals/ebiom/article/PIIS2352-39...