Introduction
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an RNA virus that usually causes mild respiratory illness (Corona virus disease; COVID-19) in humans. Severe illness can develop, especially in high-risk populations, such as elderly, immunosuppressed patients, and patients with comorbidities.
The SARS-CoV-2 virion has four structural proteins known as the spike, envelope, membrane, and nucleocapsid proteins; the nucleocapsid protein holds the RNA genome, and the spike, envelope and membrane proteins create the viral envelope1.
Diagnosis of SARS-CoV-2 infection is based on reverse-transcription polymerase chain reaction (RT-PCR) performed on nasopharyngeal samples2. Serologic tests may also be used for COVID-19 diagnosis. Anti-spike IgG and IgM and anti-nucleocapsid IgG detection kits are commercially available. Time from positive SARS-CoV-2 nasopharyngeal swab correlated with SARS-CoV-2 IgG antibody levels and antibody titers gradually decline within 6-9 months, until stabilization3.
The effect of pregnancy on humoral response to SARS-CoV-2 infection as well as the rate of vertical transmission are not fully understood. At the beginning of the current COVID-19 pandemic, evidence pointed to a lack of vertical transmission, as determined by amniocentesis, umbilical cord blood, placenta, neonatal secretion and breast milk sampling4-9. However, recent data, mostly from case reports and case series, demonstrated the presence of SARS-CoV-2 in the placenta10-12, positive RT-PCR of nasopharyngeal swabs of newborns and evidence of seropositivity in neonates13-17.
Evidence for vertical transmission is suggested in either positive neonates for SARS-CoV-2 RT-PCR, the presence of IgM-type antibodies in the newborn since these antibodies do not cross the placenta, and positive neonatal IgG serology with seronegative mother.
The present study explored maternal humoral immune responses to SARS-CoV-2 infection and the rate of vertical transmission.