No, Chinese scientists did not ‘create COVID-19 strain that is 100% lethal’

It’s been four years since the COVID-19 virus first began to spread. The U.S. National Intelligence Council assessed that two theories on the virus’s origins are plausible: natural exposure to an infected animal or a laboratory-associated incident.

Recent alarming headlines of Chinese experiments involving the virus reignited pandemic-era fears online.

VERIFY reader Karen asked us on Facebook if a story from the Staten Island Advance, a newspaper local to New York City’s Staten Island, titled “Chinese scientists create COVID-19 strain that is 100% lethal to ‘humanized’ mice, report says” is true. Similar headlines have appeared on other news sites like the New York Post.

THE QUESTION

Did Chinese scientists create a COVID-19 strain that’s 100% lethal to mice?

THE SOURCES

• Viral study titled “Lethal Infection of Human ACE2-Transgenic Mice Caused by SARS-CoV-2-related Pangolin Coronavirus GX_P2V(short_3UTR)”

• Posts made to ScienceCast, a forum for researchers to discuss studies, by Lihua Song, Ph.D., one of the scientists who worked on the study

• Studies of the same virus published in March 2020, December 2022 and January 2023

• Bacterial and Viral Bioinformatics Resource Center (BV-BRC)

• The Jackson Laboratory

THE ANSWER

No, Chinese scientists did not create a COVID-19 strain that’s 100% lethal to mice.

Chinese scientists did recently conduct a study in which they cloned a coronavirus, not a COVID-19 strain, that killed all four mice that were infected with it. However, this is not consistent with past studies, and the researchers say it does not mean it would kill humans.

WHAT WE FOUND

A group of Chinese scientists, the majority of which are affiliated with the Beijing University of Chemical Technology, recently pre-printed a study — meaning they’ve published it online before it has been reviewed by peers to confirm it’s scientifically sound — titled “Lethal Infection of Human ACE2-Transgenic Mice Caused by SARS-CoV-2-related Pangolin Coronavirus GX_P2V(short_3UTR).”

The scientists did not create a mutant COVID-19 strain to conduct this study, as some of the headlines suggest, nor did they use COVID-19 at all. Instead, the scientists studied a different coronavirus using just four mice. Coronaviruses are a family of viruses that include COVID-19, but also strains of the common cold. 

The study’s authors clarified that the mouse infections in the study do not mean the virus would also kill humans. The exact same virus has been the subject of other studies, including those in which the virus infected similar kinds of mice. The mice in those other studies did not die. 

First, we’ll explain why the claim that the scientists “created a COVID-19 strain” is false. Then we’ll add context to this coronavirus’s lethality to mice — both in this study and in similar studies.

Chinese scientists did not create a COVID-19 strain

The scientists explain within the text of the study that they worked with a coronavirus, which is a family of viruses that includes COVID-19, but not COVID-19 itself. This coronavirus, which they called GX_P2V, was a sample they found in an animal called a pangolin in 2017, according to the scientists.

The virus used in the study was first collected in 2018, according to an earlier study by researchers from Hong Kong and Beijing. Its collection date is confirmed by the Bacterial and Viral Bioinformatics Resource Center (BV-BRC), which shows it was one of six related viruses collected from pangolins by researchers at the time. 

The virus began adapting, or mutating, after it was first collected, according to a study published in December 2022. The study’s researchers, some of whom later worked on the viral lethal mouse study, said the virus “rapidly adapted” to a kind of animal cell commonly used as a host for viruses studied by scientists.

Lihua Song, Ph.D., one of the scientists who worked on the viral lethal mouse study, explained on ScienceCast, a forum for researchers to discuss studies with other scientists, that the sample they used is a clone of the virus sample that mutated between 2018 and 2022.

Scientists no longer have an original, unmutated version of the virus because the original sample adapted in the animal cell, Song explained. Song suspected that the original pangolin sample mutated because it had difficulty growing in the animal host cells used by scientists

Putting “100% lethal to ‘humanized’ mice” claim in context

The scientists in the viral study used a small sample size of mice: 12 in total, four of which were infected with the virus. All four of the infected mice died, but the researchers noted that the virus did not kill similar mice in other studies.

The mice used in the study were “ACE2 humanized” mice. These kinds of mice, according to the Jackson Laboratory, are “humanized” because their cells have “human ACE2, the receptor used by severe acute respiratory syndrome coronavirus (SARS-CoV) to gain cellular entry.”

“While GX_P2V(short_3UTR) proved lethal in our mouse model, it's important to consider that it did not cause disease upon infecting two other distinct ACE2 humanized mouse strains,” Song said on ScienceCast.

Song is referring to a January 2023 study that said it infected three groups of mice, two of which were groups of humanized ACE2 mice. The researchers noted that the infected mice “presented no obvious clinical symptoms,” leading them to believe that GX_P2V may not be very good at causing disease. 

Song and the other researchers in the viral study wrote that the reason the virus was so lethal may have been because their mice had abnormally high ACE2.

“It is very likely that the high pathogenicity of GX_P2V C7 in our hACE2 mice is due to the strong expression of hACE2 in the mouse brain,” the researchers wrote. “Under normal circumstances, both human and mouse brains exhibit low expression of ACE2.”

The researchers said that because of this “mouse infections in this study have no correlation with human infections.”

The scientists said the purpose of the study was to assess a potential candidate for use in vaccines or drugs meant to protect against broad groups of coronaviruses.