Introduction
Despite swift advances in our understanding of the SARS-CoV-2 virus, much remains to be understood regarding the timing, nature and persistence of both the humoral and cellular human response. Confirmation of an antibody response in pregnant women can direct resources in maternal services but also in the management of neonates during future surges in a similar fashion that current antenatal influenza and pertussis vaccination schedules utilise the transplacental migration of antibodies to enhance the neonatal immune system (1).
In this study, we present a comprehensive profile of the temporal serological response in pregnant women and document the presence of transplacental antibodies to SARS-CoV-2.
Maternal IgG antibodies travelling across the placenta, provide vital immunity to the new-born and have been demonstrated in infants for infections such as tetanus and human papillomavirus (HPV) (2, 3). To date, the evidence is sparse surrounding transplacental passage of SARS-CoV-2. Initially, at the outset of the pandemic, strict measures were adopted to reduce the risk of vertical transmission to the neonate, including isolation of babies from SARS-CoV-2 positive mothers (4). Antibodies have been demonstrated in the blood of neonates born to positive mothers when tested at birth (5, 6) and evidence of maternal antibodies to SARS-CoV-2 within cord bloods is slowly emerging though data is sparse(7, 8). Further confirmation of transplacental migration of maternal anti-SARS-CoV-2 antibodies in umbilical cord blood, could suggest the possibility of passive immunity and could even direct future vaccination protocols in pregnant women.
Determining the seroprevalence of SARS-CoV-2 has largely been based on detection of viral RNA using reverse transcription polymerase chain reaction (RT-PCR). Detection rates can be affected by collection and storage of the specimen with varying results reported depending on testing of saliva, nasal, nasopharyngeal specimens or rectal (9, 10, 11, 12, 13) Therefore, detection of antibodies against SARS-CoV-2 (IgM or IgG) in serum is likely to provide a more accurate estimation of the cumulative prevalence of SARS-CoV-2 in a population.
Population-based data on SARS-CoV-2 infection in pregnancy and assessment of passive immunity to the neonate, is lacking. The aim of our study was to characterise the immune response to SARS-CoV-2 in a cohort of symptomatic and asymptomatic pregnant women. We assessed SARS-CoV-2 in pregnancy with combination of RT-PCR and, using three independent assays, serological detection of anti-SARS-CoV-2 antibodies. In addition, we obtained umbilical cord blood samples to matched RT-PCR positive or serological positive mothers and therefore we also present evidence of transplacental passage of anti-SARS-CoV-2 antibodies.