evidence: Nasal swabs are used to collect biological samples from the back of the nasopharynx in order to test for the presence of SARS-CoV-2 infection. The nasal swab has to be inserted far into the nasal cavity until it reaches the nasopharynx located behind it. The human brain is separated from the nasopharynx by several layers of hard tissue, including bone. It is therefore not possible for nasal swabs to reach the brain or the blood-brain barrier.