Medical professionals are often taught these days that aspiration is not necessary for IM injections, particularly in commonly used sites such as the delts.
From the CDC [1]: Aspiration before injection of vaccines or toxoids (i.e., pulling back on the syringe plunger after needle insertion but before injection) is not necessary because no large blood vessels are present at the recommended injection sites
From the CDC [1]: Aspiration before injection of vaccines or toxoids (i.e., pulling back on the syringe plunger after needle insertion but before injection) is not necessary because no large blood vessels are present at the recommended injection sites
[1] https://www.cdc.gov/vaccines/hcp/acip-recs/general-recs/admi...