In this preprint, Andersson et al. assessed whether blood samples obtained from patients with COVID-19 carry active infectious SARS-CoV-2 RNA. A systematic review of 22 recently published preprints combined with the authors’ own patient data (424 individuals) showed that 10% of blood samples taken within 28 days of symptom onset contain SARS-CoV-2 RNA at low copy number, but no sample exceeded the threshold for viral infectivity. Incubation of VeroE6 cells with SARS-CoV-2-RNA-positive serum samples from patients did not reveal any cytopathic effects or lead to viral replication. Further studies will be required to determine the safety of blood samples to inform changes to biosafety policies.