There are many different concerns. I havent done a rigorous meta-analysis but they also come from very respectable scientists.

> https://www.businessinsider.com/coronavirus-vaccine-may-be-i...

https://www.telegraph.co.uk/global-health/science-and-diseas...

And notice that there haven't been very exciting news from the vaccine developmnent trials. If anything there were more setbacks than pleasant surprises.

There were concerns because SARS vaccine attempts hadn't been further developed due to apparent cytokine storm problems. I think we're far enough along to be confident that that isn't an issue with vaccines for this virus.

Some people also make a comparison to the common cold coronaviruses which have a lot of strains and might be rapidly mutating. Honestly, it's a bad comparison because it's clear this coronavirus isn't mutating rapidly, and besides we haven't really tried to target common cold coronaviruses - why would we when rhinoviruses are the most frequent cause of the common cold?

There's a bit more to it. The reason vaccines weren't developed previously for other coronaviruses is because in trials for a RSV vaccine, 80% of treated kids that got infected needed hospitalisation and two died, while something like 5% of the control infections needed hospitalisation. Due to antibody-dependent enhancement.

So yes there are immunopathology concerns with eliciting a T-cell response, and inducing a humoral immune response has the potential to make things worse.

That's why most trials take a look at the Th1 vs Th2 response to see if there's any indication of ADE. The currently available data do not seem to point to that.