Maternal COVID-19 Injections Significantly Reduced Child Hospitalizations During Omicron Wave

In a recent study published in the CDC MMWR and Weekly Morbidity and Mortality Report, a group of researchers evaluated the protective effect effectiveness of Maternal coronavirus disease 2019 (COVID-19) vaccination during pregnancy against COVID-19-related hospitalizations and severe outcomes in infants younger than six months during the prevalence of the Omicron variant.

Study: Effectiveness of Maternal COVID-19 mRNA Vaccine During Pregnancy Against COVID-19-Associated Hospitalizations in Infants <6 Months During SARS-CoV-2 Omicron Prevalence: 20 States, March 9, 2022 as of May 31, 2023. Image Credit: mentalmind/Shutterstock

Background

COVID-19 during pregnancy can cause unfavorable pregnancy and neonatal outcomes. However, it has been shown that maternal vaccination transfers vaccine-induced antibodies to the fetus, thus preventing serious childhood outcomes related to the virus. Maternal vaccination was previously estimated to be 38% effective against COVID-19-related hospitalizations in infants <6 months during the prevalence of Omicron (December 2021 to March 2022). More research is needed to continually update and understand the evolving efficacy of maternal vaccination during different stages of pregnancy and against emerging variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to optimize the protective benefit for both mothers as well as babies.

About the study

The Overcoming COVID-19 Network conducted a large study using a case-control design to evaluate vaccine efficacy (VE) in infants under six months of age, using methods that have been described previously. The present study, conducted between March 2022 and May 2023, focused on infants hospitalized in 26 hospitals due to acute COVID-19 and included those who tested positive for SARS-CoV-2, as well as infants of control that had a disease similar to COVID-19. but it was negative.

The study examined the implications of maternal receipt of at least one dose of the COVID-19 mRNA (messenger ribonucleic acid) vaccine during pregnancy, contrasting data from vaccinated and unvaccinated mothers. It excluded infants whose mothers had inconclusive vaccination status or timing, ensuring the reliability of the analysis. This investigation occurred during the circulation of multiple Omicron subvariants, which were meticulously identified.

Maternal vaccination statuses were categorized based on whether mothers had received vaccines before or during pregnancy, considering both mRNA and viral vector vaccines. The precise timing of vaccination and subsequent intervals until hospitalization of the infants were rigorously calculated.

VE was then calculated, focusing on several influencing factors, including demographic characteristics and hospital admission details, using robust statistical models and software. A secondary examination of the VS was also performed in infants younger than 3 months. This meticulous activity complied with all relevant laws and policies and was sanctioned by the Centers for Disease Control and Prevention (CDC), ensuring compliance with research ethics and protocols.

Study results

In the present study conducted between March 2022 and May 2023, among 1,076 hospitalized infants, 360 (33%) were excluded, mainly because their mothers received the most recent vaccine dose before pregnancy. Consequently, 716 hospitalized infants were included, of which 339 control patients and 377 case patients with a median age of 2.3 months. Among them, 153 (21%) had at least one underlying health condition and 162 (23%) were born premature.

Among the 377 case patients, 22% were born to women who had received one dose of the COVID-19 vaccine during pregnancy, compared to 28% in control patients, illustrating a notable correlation between maternal vaccination and reducing child hospitalization. Vaccine receipt times were primarily within the first 20 weeks of pregnancy in both groups. Both groups showed similarities in demographic data, prevalence of premature births, and presence of underlying health problems, although the prevalence of heart problems was higher among case patients.

The present study found a substantial median interval of 236 days between receipt of the most recent vaccine dose and subsequent childhood hospitalization. The VE of receiving at least one dose of the COVID-19 vaccine during pregnancy versus COVID-19-related hospitalizations was 35% among infants younger than six months. Surprisingly, VE increased to 54% among infants younger than three months, with a median interval of 219 days between maternal vaccination and infant hospitalization.

Critical analysis of the 377 patient cases revealed that 23% were admitted to an Intensive Care Unit (ICU) and 13% required critical care, demanding life support. Distinctively, the mothers of 84% of critically ill infants were unvaccinated, underscoring the paramount importance of maternal vaccination. Invasive mechanical ventilation was more common among babies whose mothers were not vaccinated, in stark contrast to those born to vaccinated mothers. Notably, the majority, 77%, of case patients had no reported underlying health problems. Among these healthy infants, the patterns were consistent; Infants of unvaccinated mothers exhibited higher critical conditions and invasive mechanical ventilation.

Conclusions

The current study revealed that infants younger than six months whose mothers received at least one dose of COVID-19 during pregnancy had a reduced risk of COVID-19-related hospitalization, particularly in the first three months of life. Of the 377 babies hospitalized with COVID-19, 78% were born to unvaccinated mothers. These findings emphasize the important protective benefits of maternal vaccination, especially for infants too young to be vaccinated, without increasing the risk of adverse outcomes. This highlights the importance of maternal vaccination in reducing severe COVID-19 outcomes in infants.