Review of Research Studies on COVID-19 Vaccination During Pregnancy

A recent review article by Martina Badell et al. entitled “COVID-19 vaccination in pregnancy” published in British Medical Journal reviewed existing research on COVID-19 vaccinations. The review provides a useful review of information on this topic to date. Although it was written for clinicians and researchers, this information is also useful for individuals who are pregnant and their family members. This article offers some of the key findings and themes from the literature review in less technical language than the review.

The article reviewed the guidance from different countries and the World Health Organization or WHO (which represents numerous countries) for pregnant women considering whether they should take a COVID-19 vaccine. The current recommendation from the WHO, US CDC (Centers for Disease Control and Prevention), and US professional organizations is for pregnant, postpartum, and lactating women to receive COVID-19 vaccination. The WHO indicates that pregnant women should have access to vaccines listed on the WHO Emergency Use Listing of approved vaccines and that the benefits of vaccination outweigh the potential risks. The data in this extensive literature review supports that overall recommendation.

Rationale for the Literature Review and Overall Approach

Most of the clinical trials on COVID-19 vaccinations did not include pregnant women. Thus, data from these clinical studies addressed the needs of most people but not pregnant women. Based on prior vaccination studies of pregnant women, some clinicians offered the vaccine to pregnant women. This created information on the vaccines impact on pregnant women. This data supported the idea that benefits outweighed the risks. However, these studies were not well-designed studies that provide the best data for clinicians. Thus, numerous studies performed, and many are currently being performed or planned. There are numerous gaps in our knowledge on how well these vaccines were for pregnant women, various risks to them, the best timing, number of vaccines needed and more. This literature review was performed to offer a better understanding of what the gaps are in current knowledge with the hope of assisting clinicians and researchers in better understanding the current state of knowledge in this area. The literature review assesses 83 research articles and focuses on evidence related to the effectiveness of the vaccine, how the immune system of pregnant women responds to COVID-19 vaccines, transfer of immune protection to a fetus or newborn, and any risks that the vaccines pose to pregnant women.

Incidence / Prevalence

One area where there is a need for more research is the data on how many pregnant women have been infected by COVID-19, died from COVID-19, and how many are being vaccinated. Worldwide, this number of women infected by COVID-19 is not clear, but believed to be in the millions based on the fact that roughly 400 million people have been infected worldwide and roughly 5% of those are believed to be pregnant. In addition, US data offers a few of vaccination rates. According to the review, as of April 2022, the US Vaccine Safety Datalink “estimated that only 69.4% of pregnant women aged 18-49 years had been fully vaccinated with COVID-19 vaccines before or during pregnancy.”

Pregnancy as Risk Factor

The literature review demonstrated that pregnancy is a risk factor for severe COVID-19 infection. Being pregnant and getting COVID-19 leads to higher levels of hospitalizations, intensive care unit admission, and the need for ventilation compared to nonpregnant women. Having COVID-19 during pregnancy has been connected to a greater risk of stillbirth and maternal death. Also, other pregnancy risks (such as older maternal age and diabetes) combined with COVID-19 infection leads to even worse outcomes for pregnant women.

Immune Response and Effectiveness

The literature review also determined that COVID-19 vaccination of pregnant women can reduce problems related to the disease and any deaths to mothers or infants that can arise from the disease. This data does not address some of the recent variants for which new vaccines are being developed – some of which are being tested in pregnant women. In addition, the data on effectiveness only rises from a few of the existing vaccines. The researchers writing the literature review call for more data on all vaccine types especially those more commonly used in low income countries. There is also a need for more data on the timing of COVID-19 vaccinations. Despite this lack of data, most countries recommend vaccination at all stages of pregnancy since the goal is to prevent infection at any stage and prevent harm to the fetus and infants. The review also points out that 11 new clinical trials are planned that will offer data on the safety and effectiveness of COVID-19 vaccinations in the future.

Immune Response

Overall, the literature review found that the immune response to COVID-19 vaccines for pregnant and nonpregnant women was similar, but as stated, the data on the timing of the vaccine for pregnant women remains unclear. There were some studies identified however that showed a lower immune response for pregnant women than nonpregnant women. The literature review authors attribute this to variation among different populations. One challenge with the studies is that the vaccines are being given at different times and for pregnant women with varying disease states, so there remains a need for more research.

Another finding regarding immune response is that it transfers over to the fetus and infant. The researchers found that the degree of immune protection transferred to the fetus seems to depend on the level of the mother’s immune response and this depends on the timing of vaccination. Better understanding of these steps was viewed as an area of future research.

Side effects

The researchers were clear in indicated that studies to date monitoring pregnant women who received COVID-19 vaccines have not identified any pregnancy specific safety concerns. Based on a review of 26 studies, the overall rates of adverse perinatal outcomes were “not increased after maternal vaccination.”

Future Work

As stated above, there are numerous areas of research left to explore to guide COVID-19 vaccinations for pregnant women. With the recent indication from the White House that an annual COVID-19 vaccine may be required, more data will be critical to guide the decisions of patients and their clinicians.

Perry Payne
Dr. Perry Payne is a public health practitioner and scholar with expertise in quality of care, health equity, prescription drug policy, and health care ethics. He has over ten years of experience as a freelance health care/medical writer and editor. His full-time work experience includes working as a professor and researcher in universities, serving as a federal government official, and a brief stint working for healthcare technology companies.

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