The AstraZeneca vaccine is based on an adenovirus vector, which has never been approved for use in humans. It uses a weakened live virus that can (and apparently has, in the case of the J&J vaccine, which is using very similar tech) cause serious adverse systemic reactions. From what we've seen so far, the safety profile for these vaccines is far worse than the mRNA/lipid nanoparticle based vaccines coming from Moderna and Pfizer/Biontech.
It's also not really news. We know that a vaccine will prompt an immune response. Dozens of others in progress have already shown this with phase 1 and phase 2 data. The question is how strong, how long lasting, and how safe is it, along with the question of real world efficacy data from placebo controlled trials.