Dr. Bhakdi is concerned with the side effects as well as believing any vaccine
is not going to effective against coronaviruses.
Here's one of his interesting presentations on the subject:
"Immunity & Immunization by Prof Sucharit Bhakdi"
View: https://youtu.be/4uo2KGiSjrw
States T-cell cross immunity from T-killer/helper cells can last for years and protects far longer than any antibodies from coronaviruses could. Believes ~85% of the German population is already sufficiently protected against Covid-19 from previous exposures to coronaviruses (he discusses the risks with the gene-based vaccines toward the end of the lecture).
The other problem is the current clinical trials have
excluded many of demographics that have a much higher risk of death & complications from the virus (i.e. elderly, comorbidities). For example, you referenced Moderna; on the ClinicalTrials.gov site their exclusion criteria
excludes those over 55, obesity and those with significant medical or psychiatric conditions such as respiratory conditions (e.g, COPD, asthma), heart disease including previous coronary surgery, autoimmune diseases, etc.
So, testing these vaccines on healthy younger people isn't going to determine if they're
safe and effective for the target group that needs and is demanding protection.