Medical researchers with the Chinese army engineered mice with humanized lungs in 2019 to test viruses on them, it has been reported.

The mice, developed using CRISPR gene-editing technology, were mentioned in an April 2020 study which researched their susceptibility to SARS-CoV-2, the virus that causes the COVID-19 illness, Vanity Fair revealed in its bombshell investigation.

Of the study's 23 co-authors, 11 of them worked for the Academy of Military Medical Sciences, the medical research institute for the Chinese army.

Investigators with the U.S. National Security Council, researching the origins of the pandemic, determined that the mice referenced in the study were created in the summer of 2019 – just months before the emergence of the pandemic.

The National Security Council investigators also reportedly believed they had 'uncovered important evidence' supporting the theory that COVID-19 had leaked from a lab and began reaching out to other federal agencies, Vanity Fair reported.

'We were dismissed. The response was very negative,' said Anthony Ruggiero, the a senior director at the National Security Council.

Shi Zhengli, the Wuhan Institute of Virology lead researcher on coronaviruses known as the 'Bat Woman' for her research on bat viruses, appears to have tested at least two novel coronaviruses on humanized mice in the last three years, Vanity Fair also revealed – citing comments she made to a scientific journal and grant information.

Shi has refuted claims that COVID-19 leaked from a lab at the Wuhan Institute of Virology and that the facility conducts military research.

However, Shi was interviewed in a Scientific American article, first published in March 2020, in which she recounted how she 'frantically went through her own lab's records from the past few years to check for any mishandling of experimental materials, especially during disposal.'

Shi was relieved when none of the genetic sequences from patients with COVID-19 matched those of the viruses her team had sampled from bat caves.

'That really took a load off my mind. I had not slept a wink for days,' Shi told the outlet.

In January, the State Department released a fact sheet slamming the Chinese Communist Party of 'systematically' preventing a 'transparent and thorough investigation of the COVID-19 pandemic's origin.'

The State Department acknowledged in the fact sheet at the time that the virus 'could have emerged naturally from human contact with infected animals.'

'Alternatively, a laboratory accident could resemble a natural outbreak if the initial exposure included only a few individuals and was compounded by asymptomatic infection,' the fact sheet reads.

The State Department noted that the Wuhan Institute of Virology has 'collaborated on publications and secret projects with China's military' while 'presenting itself as a civilian institution.'

'The WIV has engaged in classified research, including laboratory animal experiments, on behalf of the Chinese military since at least 2017,' the sheet reads.