J&J simply had a different delivery mechanism. It used an adenovirus which contained the same payload as the mRNA vaccines.
All four of the vaccines basically work the same way, but there's one less component involved with the mRNA versions.
Whereas the viral vectors use another virus to give our cells the info they need to make the spike protein, mRNA dumps the genetic code in directly, without using another virus as a vessel.
J&J simply had a different delivery mechanism. It used an adenovirus which contained the same payload as the mRNA vaccines.
https://www.bnnbloomberg.ca/how-j-j-and-astrazeneca-differ-from-the-mrna-vaccines-from-pfizer-and-moderna-1.1589765