Fig. 3: Effectiveness of maternal natural immunity and hybrid immunity against infant COVID-19-related hospitalization during the first 180 days of life, stratified according to maternal COVID-19 infection timing.

Cox proportional hazards models were used to estimate the hazard ratios (HR) and 95% confidence intervals (CI) for COVID-19 hospitalizations in the Hybrid and Natural groups of maternal immunity status, compared to the maternal naïve group, stratified by maternal infection timing. Infection before pregnancy is defined as the last infection that occurred before conception of pregnancy. Infection before 20 weeks refers to the last documented infection that occurred during the first 20 weeks of gestation, while infection after 20 weeks refers to the last documented infection that occurred during the last 20 weeks of gestation. Models were adjusted for maternal age, gestational age at delivery, parity, and neonatal sex; multifetal gestation, birthweight, and number of maternal documented SARS-CoV-2 tests during pregnancy. Maternal Immunization effectiveness was calculated as (1−adjusted hazard ratio) × 100. Case infants, n = 661; Control infants, n = 59,460. Boxes and error bars represent the median and 95% CI. Dotted line shows no effect point. Subgroups are indicated by color: Hybrid, red; Natural immunity, green. (Delta and Omicron waves were analyzed separately; results are shown in Supplementary fig. 4A, B).