Short-lived neutralizing activity against SARS-CoV-2 in newborns of immunized mothers

Newborns under 6 months of age are at high risk of hospitalization for acute respiratory failure following SARS-CoV-2 infection. Herein, we analyzed neonatal protection against SARS-CoV-2 passively acquired after mother vaccination and/or infection (hybrid immunity).

We enrolled seventy-eight newborns of immunized mothers against SARS-CoV-2 before or during pregnancy, through vaccination and/or infection. Infants were stratified based on the anamnestic lack (SARS-CoV-2 Vaccinated - SV)/presence (SARS-CoV-2 Infected and Vaccinated - SIV) of COVID-19 maternal infection. SARS-CoV-2-specific Neutralizing Activity (NA) in plasma was assessed by virus neutralization assay (vNTA) against the SARS-CoV-2 Omicron strain at delivery (T0), 3 and 6 months after birth (T3 and T6). Cytokine and chemokine profiles in newborns were also analyzed.

At birth, significantly lower NA was observed in infants of SV compared to that of SIV mothers; NA declined equally in both groups 3 months after delivery. The presence of at least 4 immunizing events in the mother significantly enhances the NA against SARS-CoV-2 in newborns, regardless of the type of immunization (vaccination or hybrid immunity) and of the timing of the last maternal immunization. Finally, cytokines and chemokines plasma levels were high at birth in all newborns, followed by a decline over the subsequent month.

Our findings suggest that, independently of a previous SARS-CoV-2 infection or vaccination, it is reasonable to upgrade the recommendation of a booster dose during pregnancy to a "strongly recommended" status, with a view to conferring protection to newborns in the first months after delivery.