If you take an intramuscular injection without aspirating the needle to make sure it's not found a blood vessel in the deltoid, you risk cardiovascular damage pointlessly. The standard of practice is so absurd and flawed yet its going to take years longer before people like you become aware of how badly we've been mislead.
One mouse study found that vaccine injection without aspiration did significantly increase the risk of adverse cardiac events. That research hasn't been reproduced in humans but this area deserves further investigation. At least early in the pandemic, US healthcare providers weren't routinely aspirating.
I don't know the injection practices in Germany. The WHO and US CDC no longer recommend aspiration prior to intramuscular injection, mainly over pain management concerns. (I'm not claiming this is a good idea, just pointing out the current injection protocol.)
In practice there is a wide variance between US healthcare providers depending on where they work and how they were trained. Some aspirate, some don't, some try but use the wrong technique.
