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Coronavirus disease 2019 (COVID-19) mRNA vaccines generated “robust” humoral immunity in pregnant and lactating women, with immunogenicity and reactogenicity similar to that observed in non-pregnant women. In addition, immune transfer to neonates was found to occur via placenta and breastmilk, according to study data published in the American Journal of Obstetrics and Gynecology.
These findings came from a prospective cohort study involving 131 reproductive-age women (84 pregnant, 31 lactating, and 16 non-pregnant) who received the COVID-19 mRNA vaccines. Of the pregnant vaccine recipients, the mean gestational age at first vaccine dose was 23.2 weeks and 13 delivered during the study timeframe from December 17 to March 2, 2021.
Titres of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike and receptor binding domain immunoglobulin (Ig)G, IgA and IgM were quantified in participant sera (n = 131) and breastmilk (n =31) at baseline, at the time of second vaccine dose, 2-6 weeks post second vaccine, and at delivery. Titres were compared to those of banked sera from 37 pregnant women infected with SARS-CoV-2 in pregnancy and enrolled between March 24, 2020 and December 11, 2020. Researchers also assessed umbilical cord sera (n = 10) titres at delivery.
Study data showed that vaccine-induced antibody titres were equivalent in pregnant and lactating women compared to non-pregnant women (median [interquartile range {IQR}] 5.59 [4.68-5.89] in pregnant women, 5.74 [5.06-6.22] in lactating women, 5.62 [4.77-5.98] in non-pregnant women; P = 0.24). The researchers found that all titres were significantly higher than those induced by SARS-CoV-2 infection during pregnancy (P< 0.0001).
On the other hand, vaccine-generated antibodies were present in all umbilical cord blood and breastmilk samples. Neutralising antibody titres were found to be lower in umbilical cord compared to maternal sera, although this finding did not achieve statistical significance (median [IQR] 104.7 [61.2-188.2] maternal sera, 52.3 [11.7-69.6] cord sera, P = 0.05). Further, the second vaccine dose (boost dose) was found to increase SARS-CoV-2-specific IgG, but not IgA, in maternal blood and breastmilk.
Meanwhile, no differences were noted in reactogenicity across the groups.
“This study provides the first data from a large cohort on maternal antibody generation in response to COVID-19 vaccination, compares vaccine-generated immunity to that from natural infection in pregnancy, and suggests vaccination of pregnant and lactating women can confer robust maternal and neonatal immunity,” wrote Kathryn J. Gray, MD, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, and colleagues.
“Here, robust and comparable IgG titres were observed across pregnant, lactating, and non-pregnant controls, all of which were significantly higher than those observed in pregnant women with prior SARS-CoV-2 infection,” the authors noted. “Boosting resulted in augmented IgG levels in the blood, translating to transfer of IgG to the neonate through the placenta and breastmilk.”
“The presence of neutralising antibody transfer in nearly all cords, and improved transfer with increased time from vaccination, points to the promise of mRNA vaccine-induced delivery of immunity to neonates,” the authors added. “Transfer would perhaps be optimised if vaccination is administered earlier during gestation, though this needs to be directly examined in future studies.”
The authors added that “these data provide a compelling argument that COVID-19 mRNA vaccines induce similar humoral immunity in pregnant and lactating women as in the non-pregnant population” and that the data “do not elucidate potential risks to the fetus.”
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