Now recommends aspiration. The vaccine is to be injected only intramuscular (i.m.), and in no case intradermal, subcutaneous, or intravenous. In animal models, direct intravenous injection of an mRNA vaccine has led to Myopericarditis (both clinically and histopathologically).
Although inadvertent intravenous injections are rare during application of intramuscular vaccines, aspiration of the needle is a sensible precaution when vaccinating against COVID-19 and can lead to increased safety.