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Flawed calculation fuels falsehood on Pfizer vaccine and pregnancies

August 22, 2022 GMT
Vials with the Pfizer-BioNTech COVID-19 Vaccine are seen in a cooler before being thawed at a pop-up COVID-19 vaccination site at St. Luke's Episcopal Church, Tuesday, Jan. 26, 2021, in the Bronx borough of New York. A false claim about the vaccine's clinical trial and pregnancies has spread online in recent days. (AP Photo/Mary Altaffer)
Vials with the Pfizer-BioNTech COVID-19 Vaccine are seen in a cooler before being thawed at a pop-up COVID-19 vaccination site at St. Luke's Episcopal Church, Tuesday, Jan. 26, 2021, in the Bronx borough of New York. A false claim about the vaccine's clinical trial and pregnancies has spread online in recent days. (AP Photo/Mary Altaffer)
Vials with the Pfizer-BioNTech COVID-19 Vaccine are seen in a cooler before being thawed at a pop-up COVID-19 vaccination site at St. Luke's Episcopal Church, Tuesday, Jan. 26, 2021, in the Bronx borough of New York. A false claim about the vaccine's clinical trial and pregnancies has spread online in recent days. (AP Photo/Mary Altaffer)
Vials with the Pfizer-BioNTech COVID-19 Vaccine are seen in a cooler before being thawed at a pop-up COVID-19 vaccination site at St. Luke's Episcopal Church, Tuesday, Jan. 26, 2021, in the Bronx borough of New York. A false claim about the vaccine's clinical trial and pregnancies has spread online in recent days. (AP Photo/Mary Altaffer)
Vials with the Pfizer-BioNTech COVID-19 Vaccine are seen in a cooler before being thawed at a pop-up COVID-19 vaccination site at St. Luke's Episcopal Church, Tuesday, Jan. 26, 2021, in the Bronx borough of New York. A false claim about the vaccine's clinical trial and pregnancies has spread online in recent days. (AP Photo/Mary Altaffer)

CLAIM: Pfizer documents show that 44% of pregnancies reported during its COVID-19 vaccine trial ended with miscarriages.

AP’S ASSESSMENT: False. The claim is based on a flawed calculation that, among other issues, twice counted some of the same reported miscarriages — which also were not established to be caused by the vaccine. Studies have found the vaccines do not increase the chances of spontaneous abortion.

THE FACTS: Thousands of social media users in recent days spread the erroneous claim that newly released documents showed that nearly half of all pregnancies in the Pfizer vaccine trial resulted in miscarriages.

“Massacre: Nearly Half of Pregnant Women in Pfizer Trial Miscarried,” one widely shared headline claimed.

The claim first appeared Aug. 12 in a blog run by Naomi Wolf, an author who has gained attention in recent years for spreading COVID-19 misinformation. The blog post falsely claimed that documents from the Food and Drug Administration revealed “chilling data showing 44 percent of pregnant women participating in Pfizer’s mRNA COVID vaccine trial suffered miscarriages.”

Asked for comment, the Daily Clout noted in a statement to The Associated Press that it had issued a correction. The post now states in a footnote that the 44% figure is “incorrect.”

The original blog post cited a more than 3,600-page document of Pfizer information dated March 2021 and submitted to the FDA’s Center for Biologics Evaluation and Research. The blog post pointed to 22 references in the document to spontaneous abortions, or a pregnancy loss without outside intervention before the 20th week of pregnancy. The blog also noted that a table within the same document showed 50 pregnancies that occurred among trial participants after receiving their first dose.

Using those numbers, the blog wrongly concluded that nearly half of pregnancies in the trial resulted in miscarriages.

But Jeffrey Morris, director of the division of biostatistics at the University of Pennsylvania’s Perelman School of Medicine, told the AP in an email that the post’s methodology contained “numerous mistakes.”

The blog’s 22 references to miscarriages actually count about half of the same events twice, Morris said. That’s evident by comparing the unique ID numbers of the clinical trial participants for each of the reports.

For example, a single miscarriage reported by one participant in October 2020 was recorded in a “Listing of Adverse Events” as well as a subsequent “Listing of Serious Adverse Events,” though they refer to the same instance. Such reported adverse events are also not confirmed to be caused by the vaccine, but are simply events that occurred after a participant received a shot.

Also, Morris pointed out that, of the unique miscarriage events in the document, only three of the subjects appear in the table that lists 50 pregnancies that occurred after participants received their first dose. That means the table is not a listing of all participants who were pregnant during the clinical trial, and therefore can’t be used to calculate the miscarriage rate as the website did.

Miscarriages are not uncommon: It’s estimated that about 10% to 20% of known pregnancies result in miscarriage.

The AP has previously debunked similar claims that misrepresented Pfizer data to assert that the vaccine was dangerous to pregnancies.

In reality, a 2021 study in the Journal of the American Medical Association found that COVID-19 vaccine exposure did not increase the odds of a spontaneous abortion — a pregnancy loss before 20 weeks. And a study published in the New England Journal of Medicine the same year found that the risk of spontaneous abortion after mRNA COVID-19 vaccination was consistent with the expected risk of spontaneous abortion.

A Pfizer spokesperson said the company doesn’t comment on claims on social media but noted in a statement that its phase 3 clinical study included more than 44,000 people, half of which were women, and that miscarriages were not reported as a vaccine side effect.

The FDA did not return a request for comment.

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This is part of AP’s effort to address widely shared misinformation, including work with outside companies and organizations to add factual context to misleading content that is circulating online. Learn more about fact-checking at AP.