It is an RNA vaccine. RNA is much less stable than DNA for a few reasons.
The main one is that Deoxyribose (the D in DNA) is missing an oxygen atom when compared to ribose (the R in RNA). That oxygen atom, as part of a hydroxyl group, is very reactive and tends to combine with other elements and break down the RNA quickly.
DNA is designed to be very stable and last a long time. It is nature’s long-term information storage.
RNA is designed to be used quickly and temporary. It is a set of instructions for immediate work, not storage.
it’s actually an mRNA vaccine (messenger RNA).