There is no evidence to prove the vaccine has caused any serious adverse effects so far. If that were the case, it is unlikely the Data Safety and Monitoring Board (DSMB) and U.S. Food and Drug Administration (FDA) would recommend resuming the trial.
> After a thorough evaluation of a serious medical event experienced by one study participant, no clear cause has been identified. There are many possible factors that could have caused the event. Based on the information gathered to date and the input of independent experts, the Company has found no evidence that the vaccine candidate caused the event.
https://www.jnj.com/our-company/johnson-johnson-prepares-to-...
There's also no evidence to prove that it wasn't. Furthermore, the AstraZeneca vaccine was halted for a case of transverse myelitis, a very common (and serious) adverse reaction seen in DNA/adenovirus based vaccines like ChAdOx1 [0]. These complications have not been seen at all in the mRNA based vaccines, since they do not involve a live virus.
[0] https://medcitynews.com/2020/10/report-fda-takes-closer-look....
Also, the AZ trial was given the go-ahead along with the J&J trial.
https://www.reuters.com/article/us-health-coronavirus-astraz...
The worrying trend is the ,,signed contracts with governments'' part even though the clinical trial results are not out yet. It seems that vaccination gets highly political, just like how EU made a mistake of paying for Remdesivir even though we knew that it's not worth it at that point.
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.