Figure 2. Cumulative Incidence of SARS-CoV-2 in Vaccinated vs Matched Unvaccinated Pregnant Women.

Kaplan-Meier curves were used for cumulative probability of SARS-CoV-2 infection. Follow-up for each matched pair was initiated simultaneously on the same calendar date for both the vaccinated woman and her control according to the date of the vaccinated woman’s first dose and was censored simultaneously 10 days after vaccination of the matched control to maintain groups' exchangeability over time and avoid selection bias.

Median follow-up time in both groups was 37 days (interquartile range, 21-54 days). P value for statistical comparison was estimated by log-rank test using robust variance estimator to account for matching: P < .001. Shading illustrates 95% CIs. There were no further events from day 70 to end of observation at 110 days.