https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3335060/
The study described findings of antibody-dependent enhancement with the original SARS. I am no expert, but my understanding is that when test subjects were given the vaccine, and then later 'challenged' by the SARS virus, they developed a pathological response. In other words, taking the vaccine had a potential to make their response to SARS and potentially other coronaviruses worse.
The study I linked therefore recommended caution in giving the vaccine to humans.
Obviously this is something that vaccine researchers are aware of (see https://www.nature.com/articles/s41564-020-00789-5), but I think it's something that is perfectly rational to be concerned about given the time and money pressures available with SARS-CoV-2 vaccination.
Also, there are some interesting treatments targeting the ACE2 receptors that SARS-CoV-2 binds to which looks like they are reducing mortality rates, and perhaps long-term scarring in the lungs. Among these are Vitamin-D (which people are probably nutritionally-deficient anyways), and human recombinant soluable ACE2 (basically, injecting a form of ACE2 into the body so that the virus binds to that, instead of to cells with a lot of ACE2 receptors, thus short-circuiting the replication pathway). I would be interested to see if nutritionally-sufficient vitamin-d is better at preventing severe cases of covid-19 than masking or social distancing.
My own opinion is that it is foolish to pin all the hopes on a single strategy (prevention, via vaccination), which is not guaranteed to work or guaranteed to be safe. To add forced vaccination is folly. I think it is better to see a depth of prevention and treatment options (including vaccination).