FACT CHECK: Did A Yale University Study Find That The Vaccinated Are More Susceptible To COVID-19 Than The Unvaccinated?
An image shared on Instagram claims a Yale University study found that people who are vaccinated against COVID-19 are more likely to be infected with the virus than those who are unvaccinated.
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The study referenced in the post was conducted by Danish researchers, not Yale University. While it does show negative vaccine effectiveness for the Moderna and Pfizer COVID-19 vaccines against infection from the omicron variant after 90 days, a co-author of the study explained this does not mean the vaccinated are more likely to be infected with the variant than the unvaccinated.
A post shared on Instagram shows what appears to be a headline of a news article that reads, “Yale Study: Vaccinated People MORE LIKELY to Be Infected Than Those Without Jab.” An internet search reveals the headline stems from the website Rogue Review and focused on a study that was published on medRxiv, an online archive of medical and public health studies and research that was founded, in part, by Yale University.
The study in question, “Vaccine effectiveness against SARS-CoV-2 infection with the Omicron or Delta variants following a two-dose or booster BNT162b2 or mRNA-1273 vaccination series: A Danish cohort study,” was conducted by researchers from the Statens Serum Institut in Denmark, not Yale, according to its “author information.”
The study examined the vaccine effectiveness of the Moderna and Pfizer COVID-19 vaccines against the omicron and delta variants in people after different periods of time. It found that while both vaccines provided some degree of protection against both variants in the first 90 days, effectiveness waned after this, especially against the omicron variant. In particular, it found that both vaccines had negative effectiveness against the omicron variant after 90 days, a detail the Rogue Review bases its claim on.
The study notes, however, that these findings are “arguably” indicative of “different behaviour and/or exposure patterns” in the vaccinated and unvaccinated populations and that this is possibly “causing underestimation of the VE [vaccine effectiveness].” At no point in the study do the authors state or suggest the data indicates the vaccinated are more likely to be infected with the virus than the unvaccinated.
Dr. Christian Holm Hansen, one of the study’s co-authors and an assistant professor of medical statistics and epidemiology at the London School of Hygiene and Tropical Medicine, told Check Your Fact in an email that the viral post was misrepresenting the study’s data and explained that there were “a number of reasons why the VE estimate might be negative.”
“In many places including Denmark, vaccinated individuals are tested more frequently than unvaccinated individuals,” said Hansen. “This causes the incidence rate to be higher in the vaccinated population and resultantly a negative VE estimate.”(RELATED: Did The 2009 Swine Flu Pandemic Kill 18,000 Americans?)
Hansen also noted that when officials in Denmark first identified the omicron variant, they traced many of the first instances of it in the country to international travelers and their social and professional groups – people who were largely vaccinated. He explained this may have skewed the data. “We expect therefore that there was an overrepresentation of vaccinated people among the first generations of Omicron cases identified in Denmark, not because the vaccines weren’t protective, but because the variant hadn’t spread far enough into the general population, including into the unvaccinated population, to make for comparable infection rates,” said Hansen.
He further explained that the estimation of effectiveness relied on the behavior of vaccinated and unvaccinated individuals, stating that discrepancies in risk behavior would lead to an underestimated number. He concluded his email by saying, “the vaccines’ protective effect may be low against infection with Omicron after 4 months, but it is most unlikely to be negative!”