Facebook Twitter Tumblr Close Skip to main content
A Project of The Annenberg Public Policy Center
SciCheck’s COVID-19/Vaccination Project

Social Media Claims Misrepresent Boston U. Study of What Causes Severity of COVID-19 Strains

This article is available in both English and Español

SciCheck Digest

To study the role of the spike protein in the severity of COVID-19 illnesses, researchers exposed 10 mice prone to develop severe disease to a hybrid version of the virus. Eight mice died. Social media posts say researchers created a dangerous new variant with an “80 PERCENT Kill Rate,” potentially leaving the false impression that this pertains to humans. Also, the hybrid virus used in the study had a lower mortality rate than the original virus had on mice.

Full Story

Seeing that the omicron variant of the virus that causes COVID-19 typically results in less severe disease than earlier strains, researchers at Boston University wanted to find out what part of the virus determines the severity of illness in order to improve treatment options.

They conducted a study that combined the spike protein from the omicron variant with the genome of the strain that circulated in Washington state in early 2020. The hybrid virus killed 80% of the mice used in the experiment. Researchers compared that with the effect of the unaltered Washington strain on another set of mice; it killed 100% of them. The unaltered omicron strain killed none of the mice on which it was tested.

Since the hybrid virus had a mortality rate that was similar to the original Washington strain, researchers concluded that the decisive element in determining severity is not the spike protein.

Their findings, which haven’t been peer-reviewed, were published as a preprint on Oct. 14.

But claims that distort the study’s findings have flooded social media, suggesting that the lab engineered a particularly dangerous variant of the virus and potentially leading people to wrongly believe the study found 80% of humans could be killed by it.

For example, conservative commentator Graham Allen posted a video on Instagram — where he has 885,000 followers — that claimed: “Boston University CREATES Covid strain that has an 80% kill rate?!?! WHY?!?!”

On Facebook, Dan Bongino, the conservative commentator behind one of the platform’s most popular pages, posted a video titled “Boston Lab Creates New Covid Strain With 80 PERCENT Kill Rate.”

Although Bongino acknowledged that the “kill rate” was in mice, he also suggested that researchers had created a “supervirus,” saying, “apparently they combined these two viruses to create a supervirus that kills 80% of mice.”

And the conservative outlet the Post Millennial promoted a story on Instagram with a graphic that read: “Boston University makes new COVID strain with 80 percent kill rate.”

Like similar claims on social media, all of those posts were based on an article in the British tabloid the Daily Mail. On Oct. 17, the Daily Mail published a story with this headline: “Boston University CREATES a new Covid strain that has an 80% kill rate — echoing dangerous experiments feared to have started pandemic.”

That headline misrepresents the study and reinforces the long-running but unsubstantiated theory that SARS-CoV-2 was created in a lab. As we’ve explained before, the origins of the virus aren’t known for sure, but research to date suggests that it naturally spilled over from animals to humans — either directly from a bat or, more likely, from an intermediary carrier.

In any case, the first part of the headline — which is the claim that’s been repeated widely online — is a misrepresentation of the study.

The 80% figure that the headline pulled from the research paper actually referred to the effect of the hybrid virus on mice, not people, as we noted earlier.

The type of mouse used in the experiment is prone to develop severe disease when exposed to SARS-CoV-2. That kind of mouse, called K18-hACE2, is bred for research and has been used often to study the virus over the course of the pandemic.

Of the 10 mice that the Boston University researchers exposed to the hybrid virus, eight died. That compares with 100% of six other mice in the experiment that died when exposed to the unaltered version of the Washington state virus. None of the 10 mice exposed to the unaltered version of omicron died.

So the researchers concluded that it’s not the mutations in the spike protein that have made omicron less virulent, since the version of the old virus paired with omicron’s spike protein still caused death in the mice. Rather, the severity of the disease is likely determined by another part of the virus.

The researchers referred to the hybrid virus as Omi-S, saying, “in K18-hACE2 mice, Omi-S … causes a severe disease leading to around 80% mortality.”

Following the spate of misleading claims that cited the mortality figure online, virologist Marion Koopmans, who leads the Erasmus MC department of Viroscience in the Netherlands, was one of several scientists who took to Twitter to set the record straight. She critiqued the communication strategy from the university generally, and, specifically, suggested that a change in how the paper presented that finding could have improved its reception.

The finding could have instead been summarized as: “The Omi-S recombinant has the same virulence as the ancestral strain, showing virulence … properties are not only spike-mediated,” Koopmans wrote.

Another virologist, Florian Krammer, of the Icahn School of Medicine at Mount Sinai, commented on claims about whether or not the researchers had gotten the proper permission to conduct the study with a modified virus, pointing out that other researchers have done similar experiments in which they’ve made hybrid versions of the virus, here, here and here.

Mohsan Saeed, one of the Boston University researchers who worked on the paper, made a similar point in a statement to a university publication: “Consistent with studies published by others, this work shows that it is not the spike protein that drives Omicron pathogenicity, but instead other viral proteins. Determination of those proteins will lead to better diagnostics and disease management strategies.”

Because the paper identified some funding from the National Institute of Allergy and Infectious Diseases, the university has been criticized for not seeking the proper permission for carrying out this study.

The National Institutes of Health, of which NIAID is a part, told us in an emailed statement: “[NIAID] did not review nor issue awards for experiments described in a pre-print article on SARS-CoV-2 research at Boston University’s National Emerging Infectious Diseases Laboratories (NEIDL). NIH is examining the matter to determine whether the research conducted was subject to the NIH Grants Policy Statement or met the criteria for review under the HHS Framework for Guiding Funding Decisions about Proposed Research Involving Enhanced Potential Pandemic Pathogens (HHS P3CO framework). More information about the history of oversight on research involving enhanced potential pandemic pathogens is available in this fact sheet.”

The university issued a statement that said it had “fulfilled all required regulatory obligations and protocols.”

Boston University, Oct. 18: Following NIAID’s guidelines and protocols, we did not have an obligation to disclose this research for two reasons. The experiments reported in this manuscript were carried out with funds from Boston University. NIAID funding was acknowledged because it was used to help develop the tools and platforms that were used in this research; they did not fund this research directly. NIH funding was also acknowledged for a shared instrumentation grant that helped support the pathology studies. We believe that funding streams for tools do not require an obligation to report. Secondly, there was no gain of function with this research. If at any point there was evidence that the research was gaining function, under both NIAID and our own protocols we would immediately stop and report. All research at Boston University, whether funded by NIAID or not, follows this same protocol. We are in continued conversation with NIAID leadership and program officers.

It’s notable that the study found that the hybrid virus had a lower mortality rate than the original strain. But we can’t evaluate whether researchers complied with the regulatory framework without more information from the NIH.

What we do know is that the alarmist posts circulating on social media, making the claim that researchers have created a new version of the virus with an “80 PERCENT Kill Rate,” distort the findings of the study.

Editor’s note: SciCheck’s COVID-19/Vaccination Project is made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation. The goal of the project is to increase exposure to accurate information about COVID-19 and vaccines, while decreasing the impact of misinformation.


Chen, Da-Yuan, et al. “Role of spike in the pathogenic and antigenic behavior of SARS-CoV-2 BA.1 Omicron.” bioRxiv. 14 Oct 2022.

Reimann, Nicholas. “Fox News’ Dan Bongino Leads Conservative News Resurgence On Facebook.” Forbes. 14 Jan 2022.

Tilley, Caitlin. “Boston University CREATES a new Covid strain that has an 80% kill rate — echoing dangerous experiments feared to have started pandemic.” Daily Mail. 17 Oct 2022.

McDonald, Jessica. “The Facts – and Gaps – on the Origin of the Coronavirus.” FactCheck.org. 25 Jun 2021.

McDonald, Jessica. “Navarro Falsely Links Fauci to Pandemic Origin.” FactCheck.org. 19 May 2022.

Tarrés-Freixas, Ferran, et al. “Heterogeneous Infectivity and Pathogenesis of SARS-CoV-2 Variants Beta, Delta and Omicron in Transgenic K18-hACE2 and Wildtype Mice.” Frontiers in Microbiology. 4 May 2022.

An, Dong, et al. “Protection of K18-hACE2 mice and ferrets against SARS-CoV-2 challenge by a single-dose mucosal immunization with a parainfluenza virus 5–based COVID-19 vaccine.” Science Advances. 2 Jul 2021.

Koopmans, Marion (@MarionKoopmans). “Could also have been summarised as : ‘The Omi-S recombinant has the same virulence as the ancestral strain, showing virulence is properties are not only spike-mediated‘.” 9/11. Twitter. 18 Oct 2022.

Krammer, Florian (@florian_krammer). “7)…the group got in trouble. Not because of the experiment itself, no, because they did not ask for permission. To be very clear, nature did basically the exact same experiment before. It was called XD. XD was a recombinant virus in the human population that….” 7/14. Twitter. 14 Oct 2022.

Liu, Shufeng, et al. “Spike protein-independent attenuation of SARSCoV-2 Omicron variant in laboratory mice.” Cell Reports. 13 Sep 2022.

Kurhade, Chaitanya, et al. “Neutralization of Omicron BA.1, BA.2, and BA.3 SARS-CoV-2 by 3 doses of BNT162b2 vaccine.” Nature Communications. 23 Jun 2022.

Simon-Loriere, Etienne, et al. “Rapid characterization of a Delta-Omicron SARS-CoV-2 recombinant detected in Europe.” Research Square. 4 Apr 2022.

NEIDL Researchers Refute UK Article about COVID Strain.” The Brink. Boston University. 17 Oct 2022.

Branswell, Helen. “Boston University researchers’ testing of lab-made version of Covid virus draws government scrutiny.” Stat. 17 Oct 2022.

Kaiser, Jocelyn. “Was a study that created a hybrid COVID-19 virus too risky?” Science. 18 Oct 2022.

National Institutes of Health. Emailed statement to FactCheck.org. 20 Oct 2022.