Our study showed that a third dose of the BNT162b2 mRNA COVID-19 vaccine, given at least 5 months after the second vaccine dose, provides additional protection during pregnancy against hospitalizations with a diagnosis of SARS-CoV infection. -2, and against important and severe infections. sickness. As described above, significant illness was defined as documented hospitalization with moderate COVID-19-related illness, or worse, i.e., COVID-19-related pneumonia warranting hospitalization. Severe disease was defined as resting respiratory rate > 30 breaths per minute, room oxygen saturation < 94%, or the need for mechanical ventilation and severe clinical organ failure.
Currently available mRNA vaccines were designed to prevent infection and disease caused by wild strains of SARS-CoV-2. Data from non-pregnant populations demonstrate that the efficacy of the second vaccine dose decreases over time as humoral immunity wanes and new variants emerge15,16,17,18. Our data is consistent with these reports. Previous studies have reported 98% efficacy of the second dose against hospitalization shortly after vaccination3.19. We detected reduced efficacy more than 5 months after the second dose of vaccine (61% during the Delta period and none during the Omicron period), results which could support the decline in immunity. In this setting, the third dose provided additional protection during the Delta and Omicron periods (97% and 43% protection, respectively) compared to unvaccinated patients, underscoring the benefit of the vaccine booster.
We previously showed that a third dose of BNT162b2 mRNA vaccine significantly increased anti-SARS-CoV-2 antibody titers in maternal and cord blood20. Additionally, a recent study found that a third booster dose was essential to boost neutralizing antibody capacity against the Omicron variant in mothers and neonates.21. These enhanced antibody titers may have provided additional protection against the Delta variant and afforded protection against the Omicron variant.
Focusing on significant COVID-19 illness, 5 months after the second dose, the second dose effectively protected against hospitalization complicated by significant illness (97%) and severe illness (96%) during the Delta period, but not during the Omicron period. The impact of the third booster dose was substantial during the Omicron period, effectively protecting against hospitalization complicated by significant illness (97%) and severe illness (94%). To the best of our knowledge, our results present data regarding considerable vaccine efficacy against severe COVID-19 disease during pregnancy. The fact that vaccines during pregnancy nearly eliminate the risk of severe disease has been shown to play a role in patients’ decision-making about vaccination22. Therefore, our study could help promote vaccination in pregnant women.
In the present study, we focused on the impact of COVID-19 vaccine strategy on hospitalization with a diagnosis of SARS-CoV-2 infection, rather than population infection rates. Recorded infection rates may be biased by differential rates of testing in various population subgroups, including unvaccinated patients. Indeed, our data show that unvaccinated pregnant women were significantly less likely to be tested (Table 1). However, although not performed uniformly in all maternity wards, routine testing for SARS-CoV-2 during maternity admissions was mandatory in most hospitals in Israel. Given the unbiased approach to testing, a positive SARS-CoV-2 finding during hospitalization represents a better sensor of infection burden, and so we assessed and analyzed the data accordingly.
Most previous reports have analyzed pregnancy data from a single wave of COVID-19, narrowing the observations. We analyzed data from two separate time periods, when two variants with different characteristics were dominant. We have focused the temporal margins on the periods dominated by the Delta and Omicron variants, in order to present a more complete understanding of the vaccine and to reinforce the effectiveness on different viral variants. Indeed, we found substantial differences between the two time periods, which may reflect differences in virulence, ability to evade vaccine-induced immune protection, and declining protective titers over time.
CDC and Other Health Organizations Now Recommend COVID-19 Vaccination for Pregnant Women to Reduce Risk of Severe Illness and Complications11.23. As for the general population, these recommendations include the reminder of pregnant women with a third dose of vaccine, 5 months after the second dose of vaccine. Our results provide insight into the impact of COVID-19 vaccines during pregnancy and the benefit conferred by the third, dose escalation against severe disease, and serve to strengthen recommendations to vaccinate and stimulate this population. , providing clinicians and decision-makers with critical evidence to inform consultation and decision-making.
Research on the long-term consequences of COVID-19 during pregnancy for mothers and newborns is still sparse. Initial and preliminary reports of long-term effects of maternal COVID-19 infection during pregnancy have suggested disturbing adverse neurodevelopmental sequelae24,25,26. These cases highlight the urgent need for data on measures to limit maternal infection, which can have as yet unknown harmful consequences.
Our study has several limitations. Since the study is based on data collected in the real world, no randomization was possible. People who choose to decline booster doses or refuse vaccination or avoid testing may differ in their risk behavior, demographic or obstetrical characteristics from those who choose to participate. Additionally, vaccinated groups may behave in a more cautious manner that could reduce the risk of infection regardless of vaccination. Additionally, the natural and hybrid immunity acquired in patients during the pandemic, which may not have been captured by testing in the community, may have had differential protective effects in the unvaccinated and vaccinated groups. . These are possible sources of bias that are difficult to correct in a study like ours, but which must be specified and taken into account. We also recognize that other unaccounted for individual and group differences in risk factors for severe disease or likelihood of exposure to the virus may have impacted our results. Our findings were limited to the BNT162b2 vaccine. We cannot infer whether our findings are relevant to preventing reinfection in recovering COVID-19 pregnant women or populations administering other vaccines. The decision to vaccinate during pregnancy is a balance between benefit and efficacy versus safety. We have not assessed the safety of the COVID-19 vaccine, but several other large studies have3.27, and demonstrated a favorable safety profile. Finally, we lack data on the sequencing variants of the diagnostic tests used in this study. However, the inclusion of two periods dominated by distinct variants strengthens our results.
Compared to eligible unboosted or unvaccinated pregnant women, those who received a third dose of BNT162b2 had a lower incidence of hospitalization with SARS-CoV-2 infection during the Delta period and a significantly lower incidence results related to COVID-19 during the Omicron period. Our data and analyzes provide the evidence needed to support current recommendations to vaccinate pregnant women with the third booster dose of the COVID-19 vaccine.