A group of researchers analyzed 122 pregnant women and their neonates at the time of birth after receiving mRNA based COVID-19 vaccine. All the women studied received 1 or both doses of an mRNA-based vaccine for COVID-19. Of the 122 women part of the study, 55 had received only the first dose of the vaccine while 67 women had received both doses of the mRNA vaccine by the time they gave birth; 85 women had received the Pfizer-BioNTech vaccine, and 37 women received the Moderna vaccine.
All the participants tested negative for SARS-CoV-2 on nasopharyngeal swabs using RT-PCR. None of the women reported any symptoms of COVID-19 at the time of admission for delivery. They also tested negative for antibodies against the nucleocapsid protein antigen (which ensures that the detected antibodies were not produced against a past SARS-CoV-2 infection). When tested at birth, 87 women produced only an IgG response, 19 women produced both IgM and IgG response, and 16 women showed no detectable antibody response. All the women were within 4 weeks after their first dose of the vaccine.
Over time, the number of women who had an antibody response and those who passed on passive immunity to their neonates increased. All women studied and their neonates, except for 1 neonate, had detectable levels of IgG antibodies by 4 weeks post maternal dose 1 of the vaccination. Over 43% (24/55) of neonates born to women who received only 1 dose of the vaccine had detectable IgG, and over 98% (65/67) of neonates born to women who had received both doses of the vaccine had detectable IgG.
There was a weekly increase in IgG levels in pregnant women from 2 weeks after the first dose of the vaccine, and between the 1st and 2nd weeks after the second dose of the vaccine. The results also showed that maternal IgG levels were linearly associated with IgG levels in the neonates. The study’s findings show that, in pregnant women, mRNA-based COVID-19 vaccines induce maternal antibody production by 5 days after the 1st vaccination dose and offer passive immunity to the neonate by 16 days post the first dose of maternal vaccination.
The increase in maternal IgG and the increased placental IgG transfer ratio over time indicate that the timing between vaccination and birth could be a significant factor that should be considered while devising vaccination strategies for pregnant women.