Qualitative RT-PCR and SARS-CoV-2 antibody testing
All maternal cases had SARS-CoV-2 infection confirmed by real-time reverse transcriptase polymerase chain reaction (RT-PCR) using the Chinese Center for Disease Control and Prevention (CDC) recommended assay (BioGerm, Shanghai, China) as described previously.10 Conditions for amplification included reverse transcription at 50°C for 15 min, pre-denaturation at 95°C for 15 min, and 45 cycles of 94°C for 15 seconds and 60°C for 30 seconds. A cycle threshold value (Ct-value) less than 40 was defined as positive. Neonatal nasopharyngeal and anal swab samples were collected in a subset of neonates at birth, and sent to the laboratory of the Wuhan Center for Disease Control and Prevention for detection of SARS-CoV-2 RNA by RT-PCR, as described above. IgG and IgM were analysed in blood specimens, using a novel chemiluminescent immunoassay (CLIA assays Kit, YHLO) based strictly on the manufacturer’s instructions. Cut-off thresholds for SARS-CoV-2 IgM and IgG were both 10.0 AU/mL. Sample collection, processing, and laboratory testing were based on WHO guidance14.