Immunization thresholds to change the overall level and the effect of cases on deaths by COVID-19 in pregnant and postpartum women.

Since the first officially reported case of COVID-19, the scientific community has spent much of its time understanding the dynamics of the virus. Several studies have indicated that some population segments are especially susceptible to COVID-19 complications, including pregnant and postpartum women. Although recommendations such as social distancing, proper sanitation, and the use of protection masks were crucial in slowing down the virus dissemination, the protection provided by vaccination is undeniable, especially for this particular group. Concerning deaths by COVID-19, it is natural to assume that daily deaths are related to reported hospitalized cases and to expect that, as vaccination increases, this effect gradually decreases. As far as we know, no other studies have addressed this issue. Therefore, this study introduces a novel generalized linear model with segmented interaction to fill this gap. The model was used to estimate the vaccination thresholds required to change the overall level and the daily hospitalized cases effect on daily deaths from COVID-19 in pregnant and postpartum women reported between January 3rd, 2021, and January 1st, 2022. Inference methods for the proposed model were developed. The results obtained indicate that, in the first period from May 25th to July 1st, 2021 (between 14,420 and 271,570 first doses, respectively), vaccination caused a significant gradual decrease in the effect of reported hospitalized cases on fatalities and, in a second period from July 25th to October 13th, 2021 (between 653,150 and 968,880 first doses, respectively), it induced a gradual reduction of the overall level of deaths. Using the average number of cases as a reference, during the period of observations, the expected number of deaths reduced from 6.16 to 0.36, a decrease of 94.16%. The importance of learning from COVID-19 data must be highlighted, as it provides us with critical insights to better prepare for future health crises.