False 82% miscarriage claim tied to Covid-19 vaccines traced to faulty reading of 2021 study data
Senators Ron Johnson and Rand Paul released text messages from Dr. Anthony Fauci's former government phone on Monday as part of an investigation into his pandemic-era leadership, including messages discussing vaccine safety during pregnancy. The release prompted spread of a claim that Covid-19 vaccines carry an 82% miscarriage risk, including in a since-deleted post by Senator Ted Cruz. Public health experts and multiple studies have found no increased miscarriage risk associated with Covid-19 vaccines during pregnancy.
Single source · Not corroborated
On Monday, Senators Ron Johnson of Wisconsin and Rand Paul of Kentucky released a batch of text messages retrieved from Dr. Anthony Fauci's former government phone, citing them as part of an investigation into his conduct during the Covid-19 pandemic. Among the messages was a January 2021 exchange in which Fauci said a second vaccine dose "theoretically could be associated with miscarriage in the 1st trimester," along with a criticism of a study published in the New England Journal of Medicine in April 2021.
The release became a launching point for the spread of a claim — including in a since-deleted post by Senator Ted Cruz — that Covid-19 vaccines carry an 82% risk of miscarriage. That figure derives from a faulty calculation based on a 2021 NEJM study that tracked nearly 4,000 women enrolled in a vaccine safety monitoring registry. Of those, 827 had "completed pregnancies": 712 live births, 104 spontaneous abortions, and 11 other outcomes. The researchers initially reported a 12.6% miscarriage rate using those 827 completed pregnancies as the denominator — a figure comparable to the average miscarriage rate of 10–20% cited by the Mayo Clinic.
In September 2021, the researchers issued a correction clarifying that the study's design did not permit a valid miscarriage risk estimate. The follow-up period was limited, outcomes were unknown for most of the nearly 4,000 participants, and 700 of the 827 completed pregnancies involved women who were in their third trimester at the time of vaccination. The correction noted that "any risk estimate would need to account for gestational week-specific risk of spontaneous abortion" and that "no denominator was available to calculate a risk estimate for spontaneous abortions."