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.)

https://www.cdc.gov/vaccines/hcp/acip-recs/general-recs/admi...

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.