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.