James Lyons-Weiler, Ph.D.:
JAMA provides an expert example. They nearly got away with it. But then we read it.
Let me walk you through a masterclass in how to bias a study so thoroughly that even a real risk can disappear. Not with fraud, not with data tampering—just good old-fashioned design flaws, all pointing in one direction. (I will leave it to the reader to decide on this). We’re going to talk about a study recently published in JAMA Network Open by Bernard et al. (2025), which claims that getting an mRNA COVID-19 vaccine during the first trimester of pregnancy isn’t associated with birth defects.
You might have heard this result and thought, “Well, that’s reassuring.”
Let me show you why it’s not.
The Setup: A Live-Birth Only Study
“The researchers looked at over 527,000 live-born infants in France, comparing those whose mothers got an mRNA COVID-19 vaccine in the first trimester with those who didn’t. They then looked at the rate of major congenital malformations (MCMs) and said: ‘No difference.’ Their conclusion? The vaccine isn’t teratogenic. It doesn’t cause birth defects.
Here’s the problem: They only looked at live births. That means any fetus with a severe enough defect to lead to termination or fetal death is simply not counted. And guess what? The most severe defects—the ones most likely to show up if a vaccine did have a harmful effect—are the ones most likely to lead to termination or stillbirth. Let me repeat that: They deleted the most relevant cases before the analysis even started.
We don’t need to guess how big the omission is.”
Click below to read the important details. Very important illustration of scientific bias devised to deceive.