EXCLUSIVE: Whatever happened to Pfizer’s covid vaccine trial in pregnant women?
The trial began in 2021. But over a year after the last woman was enrolled, the company just admitted it still doesn’t have the data.
When covid-19 vaccines were granted emergency authorization in Dec 2020, there was consternation over whether pregnant women should be vaccinated.
Pregnant and breastfeeding women were excluded from the original Pfizer and Moderna phase III clinical trials, so any recommendation to vaccinate them was a gamble.
The world was dealing with a novel vaccine technology, tested under ‘warp speed’ conditions, and no long-term safety data to speak of.
For this reason, the WHO did not widely recommend the covid-19 vaccine during pregnancy because of insufficient safety data. But not everyone agreed.
In January 2021, soon after the vaccine roll-out commenced, US Centers for Disease Control and Prevention (CDC) updated its website saying that the mRNA vaccines were “unlikely to pose a specific risk for people who are pregnant.”
Professional societies such as the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) both advised that covid-19 vaccines not be withheld from pregnant or lactating women.
Similarly, the UK’s Royal College of Obstetricians and Gynaecologists (RCOG) released a statement saying that “COVID-19 vaccines are strongly recommended in pregnancy.”
So, as the months passed, hundreds of thousands of pregnant women globally, rolled up their sleeves to receive the vaccine, despite the absence of any clinical trials.
The message from authorities was clear – the harm from covid-19 infection outweighed any harms from the mRNA vaccine – but in truth, they couldn’t possibly have known.
Pfizer’s official product labelling information for pregnant women refers only to animal studies, stating “No vaccine-related adverse effects on female fertility, fetal development, or postnatal development were reported”.
But a freedom of information (FOI) request to the Australian drug regulator in June 2021, shows the study was only carried out in 44 rats (22 injected with 30µg of mRNA vaccine, 22 injected with saline).
The study found the vaccine led to a statistically significant doubling in fetal loss (9.77% mRNA vs 4.09% saline), but Pfizer concluded that the difference between the two groups was “not biologically meaningful.”
The label also states that Pfizer’s mRNA vaccine was not tested for its potential to cause carcinogenicity (ability to cause cancer), genotoxicity (ability to damage genetic information), or impairment of male fertility.
Unlike Pfizer, Moderna kept its pregnant rodents alive to test the embryos. Documents accessed by Judicial Watch, showed a “statistically significant” number of rats were born with skeletal variations after being injected with Moderna’s mRNA vaccine.
But Moderna concluded that the “Skeletal variations are structural changes that do not impact development or function of a developing embryo” and therefore “not considered adverse.”
In the absence of any human data, Pfizer announced it would begin recruiting volunteers for a clinical trial to examine the safety and efficacy of its mRNA vaccine in pregnant women and their newborns.
The trial, which began in Feb 2021, originally intended to enroll 4,000 women, but enrollment stopped in late 2021 with just 349 participants.
There has been no explanation for why they stopped recruiting participants, nor have the data been published in a conference abstract, preprint or medical journal.
It has been over a year since the last woman was enrolled in the trial, and all of them would have given birth by now.
Recently, Marty Makary, a public policy researcher at Johns Hopkins University, objected to the secrecy. “They should say something. They have a moral duty to speak up. Here we are 18 months later, the results of those 349 women have never been made public,” said Makary.
“They just recommended it for pregnant women with zero data. And maybe that’s why [Pfizer] stopped the study….running a study runs the risk of showing that there may not be a benefit in pregnant women,” he added.
In response to my questions, today I can reveal the reason why Pfizer hasn’t published the study — the company admitted it does not have the data.
In an email, Pfizer said the trial’s “enrollment rate declined significantly” towards the end of 2021, because authorities had already widely recommended the vaccine to pregnant women.
Declining enrollments meant that there were insufficient numbers of participants in the trial to carry out the intended analysis.
Pfizer’s full response:
In the fourth quarter of 2021, enrollment was stopped in C4591015 Study (a Phase 2/3 placebo controlled randomized observer-blind study to evaluate the safety, tolerability, and immunogenicity of BNT162b2 against COVID-19 in healthy pregnant women 18 years of age and older). This study was developed prior to availability or recommendation for COVID-19 vaccination in pregnant women. The environment changed during 2021 and by September 2021, COVID-19 vaccines were recommended by applicable recommending bodies (e.g., ACIP in the U.S.) for pregnant women in all participating/planned countries, and as a result the enrollment rate declined significantly. With the declining enrollment, the study had insufficient sample size to assess the primary immunogenicity objective and continuation of this placebo controlled study could no longer be justified due to global recommendations. This proposal was shared with and agreed to by FDA and EMA.
Pfizer does not yet have a complete data set from the maternal immunization study, C4591015. Pfizer and BioNTech plan to complete the analysis of the clinical trial C4591015 and share it with global public health regulators and seek publication or presentation as is our standard practice. It is important to note that relevant real-world evidence on the use of COVID-19 vaccines in pregnant women has been presented and published numerous times by various parties in multiple journals and forums.
The FDA said it does not comment on ongoing studies.