Protective Factors Against Infant SARS-CoV-2 Infection

ABSTRACT

Background. Transplacental and milk antibodies following maternal SARS-CoV-2 vaccination could offer infants protection against SARS-CoV-2 infection as there are no approved vaccines for this age-group. Our objective was to assess maternal and infant factors to determine if they are protective against infant SARS-CoV-2 infection. Methods. Prospective cohort starting April 2021 of lactating women immunized with first SARS-CoV-2 vaccine during pregnancy or lactation and their infants. Participants have longitudinal milk and optional blood samples collected. The primary outcome was parent-reported infant SARS-CoV-2 infection between December 1, 2021 and February 20, 2022 during the local Omicron variant wave. Infants with infection before this window were excluded. We measured anti-receptor binding domain (RBD) IgG in milk and maternal and infant blood collected from October to December 2021. For women who received SARS-CoV-2 booster vaccine, the mother and infant samples that were collected 2-4 weeks after vaccine were used in this analysis. Geometric mean titers (GMTs) were log-transformed for analysis. Factors were evaluated with univariate and multivariable logistic regression. Results. Of the 101 mother-infant pairs enrolled, 89 had clinical data during this time period;73 women had milk titers;58 mother-infant pairs had blood titers. All women received SARS-CoV-2 vaccine while pregnant (44%) or lactating (56%). 83% received a SARS-CoV-2 booster vaccine. 81% were still lactating at time of analysis. 23% (N=21) of infants had infection. On univariate analysis, no daycare (Odds ratio (OR 0.2;95% confidence interval (CI) 0.1-0.6), maternal IgG in blood >= 900 (OR0.1;95%CI0.02-0.5);and IgG in milk >= 8 (OR0.3;95%CI 0.1-0.9) were significantly protective against infant infection (Figure 1). On multivariable analysis, point estimates for milk IgG, infant blood IgG, maternal receipt of booster vaccine and no daycare were highly protective against infant infection, although only milk IgG and no daycare reached level of significance (Figure 2). Estimates are likely limited by small sample size. No daycare attendance (Odds ratio (OR0.2;95% confidence interval (CI) 0.1-0.6), maternal IgG in blood >/=900 (OR0.1;95%CI0.02-0.5);and IgG in milk >/=8 (OR0.3;95%CI 0.1-0.9) were significantly protective against infant infection. Data analyzed with univariate logistic regression with infant SARS-CoV-2 infection as the dependent variable. Milk IgG >/=8, infant blood IgG >/=900, maternal receipt of booster vaccine, and no daycare were highly protective against infant infection, although only milk IgG >/=8 (OR 0.2;95%CI0.05-1.0) and no daycare (OR 0.2;95%CI 0.1-1.0) reached the level of significance. Data analyzed with multivariable logistic regression with infant SARS-CoV-2 infection as the dependent variable. Conclusion. These data identify factors significantly associated with protection against infant SARS-CoV-2 infection, which could influence parent vaccine decision-making. (Figure Presented).