Three identified Wuhan lab researchers were found to have been ill and sought treatment at a hospital in November 2019, according to a U.S. Intelligence report.

The discovery adds a new question to growing calls for a more comprehensive investigation of whether the COVID-19 virus originated and leaked from the laboratory, according to an NBC News report.

A Department of State fact sheet last year stated that the U.S. government had reasons to believe that some Wuhan lab researchers had fallen ill with symptoms consistent with both COVID-19 and common seasonal illnesses.

WIV senior researcher Shi Zhengli earlier claimed publicly that there was "zero infection" among staff and students of SARS-CoV-2 or SARS-related viruses.

U.S. intelligence agencies had not ruled out the theory that the virus had leaked from due to a lab accident, while the other possibility is that the virus was transmitted to humans through an animal host.

China has consistently denied the COVID-19 virus escaped from a lab despite the lab not releasing any raw data or records on its work with coronaviruses in bats.

Meanwhile, one spokeswoman for the National Security Council said the Biden administration still had questions about the origin of the virus, according to a Business Insider report.

READ MORE: Ex-CDC Head Robert Redfield Believes COVID-19 Came From a Wuhan Lab 

COVID-19 Origin

The World Health Organization has said that more investigation is needed to completely rule out that the virus had escaped from the Wuhan lab.

Tedros Adhanom Ghebreyesus said that more research was needed although a lab leak was the least likely cause, according to a BBC News report.

A WHO report with Chinese experts released in March stated that the lab leak explanation was highly unlikely and the virus had possibly jumped from bats to humans.

The WHO director said that as far as WHO is concerned, all possibilities of the origin remain on the table.

The WHO report had raised concerns and urged China to provide full access to experts.

WHO investigation team leader, Peter Ben Embarek, said that his team was under political pressure. Embarek added that his team had found no evidence that any laboratories in China were linked to the outbreak.

Wuhan National Biosafety Laboratory director, Yuan Zhiming, said that The Wallstreet Journal's report was a "complete lie." The Journal had first reported the incident of three researchers falling ill in November 2019.

Yuan said that the lab has not been aware of the situation and the claims were groundless.

Pandemic Started

The coronavirus had spread in December 2019 to nearly every country, affecting the personal lives of every individual and causing a global economic decline.

The WHO had then declared it a global pandemic.

In December 2020, countries have been scrummaging to secure vaccines with some of the Western Countries starting to inoculate their citizens to its most vulnerable populations, according to to The New York Times report.

In January 2020, the first cases were confirmed outside mainland China, while Chinese authorities decided to close off Wuhan by canceling planes and trains leaving the city.

Currently, the total number of cases had reached 167 million, while deaths have peaked at 3.47 million.

READ NEXT: Growing Evidence Shows COVID-19 Leaked From Wuhan Lab, Contrary to China's Claims

WATCH: Wuhan lab staff sought care before the pandemic, a media report says - from Reuters