Coronavirus vaccines weren't tested on pregnant women — here's why that's a problem

"Pregnant immune systems are a little different … we don't have any direct data on whether it's safe," one doc said

By Nicole Karlis

Senior Writer

Published December 9, 2020 6:29PM (EST)

Ultrasound pregnancy examination of a young woman in a Medical Clinic during COVID-19 outbreak (Getty Images)
Ultrasound pregnancy examination of a young woman in a Medical Clinic during COVID-19 outbreak (Getty Images)

The Pfizer/BioNTech COVID-19 vaccine is breaking some healthcare barriers, but not all.

In less than one year, the vaccine has passed through three required phases of a clinical trial and is currently ready to be mass-produced across the world. Great Britain became the first Western Nation to vaccinate its citizens this week. As soon as this weekend, hospitals across the United States will be able to start vaccinating frontline workers, pending approval by the U.S. Food and Drug Administration (FDA).

However, there's one peculiar caveat to the Pfizer/BioNTech vaccine— and to other major vaccine trials, too: none included pregnant women in their clinical trials. Indeed, not one of the vaccines expected to be approved by the FDA in the next couple weeks, including the Pfizer/BioNTech one, have been tested on pregnant women directly, leaving a cohort of people who are vulnerable to COVID-19 with no direct information on how the vaccine will affect them or their fetuses.

"We don't know anything directly about the safety of the vaccine in pregnant or in lactating persons because they were all excluded from the vaccine trials," Dr. Melissa Simon, Director of the Center for Health Equity Transformation at Northwestern's Center at Northwestern University's Feinberg School of Medicine, told Salon in a phone interview. "The only thing that could have possibly happened, which we won't know until the data are unblinded, is if any of the participants in the vaccine trials got pregnant during the course of participating in the trial."

The exclusion speaks to a long-lived trend in America's healthcare system, in which pregnant women are actively excluded from the clinical vaccine trials and critical research in healthcare. Earlier this month, the Society for Maternal-Fetal Medicine (SMFM), a non-profit organization focused on maternal health, released a statement calling the "existing practice of 'protection by exclusion'" as "harmful." The same statement said that the move has been "characterized" as "clinical experimentation on pregnant women" because it results in the vaccine being "distributed and administered without the safeguards of research protocols in place."

Simon described the intentional oversight as a "missed opportunity" and "concerning." Dr. Stephanie Gaw, PhD, an assistant professor at the University of California-San Francisco's Center for Reproductive Sciences, agreed.

"I think it was definitely a missed opportunity to get as much data as possible in order to make the most rational choices and deciding on allocation of valuable resources," Gaw said.

Fortunately, both doctors said they believe there is little risk to the fetus or pregnant women based on what we know about the technology of the COVID-19 vaccine. Multiple medical groups, including SMFM, agree. However, there are no definitive answers yet.

The Pfizer and Moderna vaccine candidates are mRNA-based vaccines, meaning they involve creating a synthetic single-stranded RNA molecule that produces proteins once in the body. In the case of the COVID-19 vaccine, these proteins are similar to those already found in the novel coronavirus and they trigger the immune system to produce protective antibodies without using parts of the real coronavirus to create immunity. According to the FDA documents, some protection against the coronavirus can occur after the first dose, while full protection occurs after the second one.

The AstraZeneca vaccine, developed by Oxford University, is slightly different from the Pfizer and Moderna vaccines in that it uses a chimpanzee adenovirus to engineer the spike protein from novel coronavirus. Simon said what we know about the Ebola vaccine in pregnant women is "one clue" that tells experts in the field that the current COVID-19 vaccines pose a "low risk" for pregnant women. According to one study on the Ebola vaccine in pregnant women, there were no congenital anomalies detected in the infants born from vaccinated women. There also wasn't an alarming gap in pregnancy loss between vaccinated and unvaccinated women.

"AstraZeneca's use of a viral vector is similar to the mechanism that has been used in the Ebola vaccine," Simon said. "But we just cannot say for sure because to our knowledge, no pregnant or lactating person has received any of the vaccines in the trials yet."

Gaw said the problem with excluding pregnant women from COVID-19 vaccine trials isn't about the vaccine itself being "dangerous" to anyone, but instead failing to protect pregnant women—especially, those who are frontline workers.

"They're making plans for deployment, healthcare workers and frontline workers will be the first to get it — but guess what, a lot of those people are pregnant," Gaw said. "We don't have any direct data on whether it's safe, we think it probably is, biologically, but we also don't know if it works the same— pregnant immune systems are a little different."

There are several reports of pregnant women — particularly those with comorbidities  — becoming critically ill from COVID-19. And according to the Centers for Disease Control and Prevention, pregnant women have a higher risk for severe outcomes of COVID-19 than those who aren't pregnant.

Gaw said the lack of data could hypothetically mean that doctors won't know the correct dosage for pregnant women.

"Is the dosing the same? Is the vaccine schedule the same in pregnancy?" Gaw explained, as one example. "On the plus side, it might be more beneficial in pregnant women; it could also protect the newborn baby and then you're vaccinating two people, there are a bunch of positives and negatives that essentially we just don't know because we're missing data at this point."

Vaccine hesitancy, which is already a problem with the pregnant and non-pregnant population, is another concern with the exclusion of pregnant women in the clinical trials.

Historically, excluding pregnant women from vaccine trials has been a "a long standing challenge," partly based on the "unsubstantiated fear" of harming a fetus, Simon said. This isn't the first time the concern of pregnant women being excluded from a vaccine trial has been raised and scrutinized before. When asked why this continues to happen, Gaw said there are usually additional barriers for including pregnant women— like more paperwork.

So, what are pregnant women—especially healthcare workers—to do?

Gaw said pregnant women should speak with their doctors, and ask for the vaccine if they want it.

"They should definitely not be excluded just because they're pregnant," Gaw said. "Ultimately, the decision relies on the patient."

The FDA documents about the Pfizer vaccine indicated that the company is expected to submit plans for a clinical study to assess safety and immunogenicity in pregnant women in the future. Until then, pregnant women seeking definitive answers are forced to wait.

By Nicole Karlis

Nicole Karlis is a senior writer at Salon, specializing in health and science. Tweet her @nicolekarlis.

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