[wuschel]

Disclaimer: It's late, and I need to confirm this statement from a immunology researcher in my network. If you are a R&D professional with the right expertise, please feel free to jump in.

There are two risks at hand here: (a) using the novel mRNA vaccine technology, and (b) using it with the SARS-CoV2 virus. While I can not say anything about the former, the aforementioned researcher in my network mentioned that as with Human papillomavirus (HPV) and other cancerogenic viruses, the SARS-CoV2 family might have tumor generating effects. Using it with a vaccine could be risky - getting infected could be risky, too.

> How worried should I be (...)

This is why we have multi stage clinical trials. Fast tracking a trial does not necessarily mean that it less testing will be done. On the contrary, the amount of resources behind these vaccine candidates are enormeous. Of course, long term effects are hard to catch. But the same applies for the long term effects of an SARS-CoV2 infection. Time and experiments will tell. Let's hope for the best.