Months before China disclosed the COVID-19 pandemic in December 2019, three researchers from the Wuhan Institute of Virology (WIV) fell ill and sought hospital care, the Wall Street Journal reported on Sunday, citing a previously undisclosed American intelligence report.

The report provides details of the number of researchers infected, the timings of their illness and hospital visits, the newspaper said. This may add weight to calls for a broader probe, after the one that was initiated by the World Health Organization (WHO) to investigate the origins of COVID-19. 

WHO’s decision-making body is expected to discuss the next phase of the investigation on Monday.

A National Security Council spokeswoman told Reuters that US President Joe Biden’s administration continues to have “serious questions about the earliest days of the COVID-19 pandemic, including its origins within the Peoples Republic of China.” She did not comment on Journal’s report.

The spokeswoman said that the US government was working with the WHO and other member states to support an expert-driven evaluation free from politicisation.

Also read: Global COVID-19 death toll up to 3 times higher than officially reported: WHO

Journal’s report said that officials familiar with the intelligence about the Wuhan lab researchers expressed a range of views about the strength of the report’s supporting evidence, with one unnamed person saying it needed “further investigation and additional corroboration.”

Meanwhile, China’s foreign ministry on Sunday said, “The US continues to hype the lab leak theory.” The comment was in response to a request for comment by the Journal.

The ministry noted that the WHO-led team had concluded a lab leak was extremely unlikely after a visit in February to the virology institute. 

A Reuters report in February said that China refused to give raw data on early COVID-19 cases to the WHO-led team, potentially complicating efforts to understand how the coronavirus outbreak began.