mRNA & thus LNP & thus spike protein (naked or in LNP or exosomes or extracellular vehicles (ECVs) in the blood long-term? Yes, the evidence has accumulated to show this, see Fertig as an example

I argue likely life-long for the mRNA (synthetic) were engineered to hide from the immune system (evade) and to have a mechanism of action long-term e.g. translate spike protein, 24/7

SOURCE:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9313234/

‘The biodistribution and pharmacokinetics of the mRNA-containing lipid nanoparticles (LNPs) in these vaccines are unknown in humans. In this study, we used qPCR to track circulating mRNA in blood at different time-points after BNT162b2 vaccination in a small cohort of healthy individuals. We found that vaccine-associated synthetic mRNA persists in systemic circulation for at least 2 weeks.’