The head of a medical school at Hong Kong’s top university has chastised a former employee for harming the reputation of her ex-colleagues when she accused them on American television of engaging in a cover-up in their coronavirus research.

The scientists were not conducting secret research or going after rumours in their studies, but were focused on urgent health issues, Professor Keiji Fukuda, director of the School of Public Health under the University of Hong Kong, said in an internal memo to staff seen by the Post.

Dr Yan Limeng, a former postdoctoral fellow at the university, had given an interview to Fox News last Friday, in which she accused the school of failing to act on her findings on the Covid-19 virus making the jump to humans.

In his message to staff on Wednesday, Fukuda, a former World Health Organisation official, suggested her so-called findings were “rumours”, adding: “I have written this note out of concern about the potential for Dr Yan’s speculations to harm the reputations of our close colleagues, who are highly respected members of our school.”

Fukuda said none of the researchers named by Yan, including Professor Leo Poon Lit-man, her supervisor, or Professor Malik Peiris, both of whom were involved in studies on Covid-19, were part of any “secret research” or cover-up, as she claimed.

“As per normal, school researchers have been involved in conducting urgent, public health research on Covid-19, rather than investigating rumours,” he wrote. “Their research was done with various mainland, Hong Kong and international collaborators, and much of it has been published.

“Over their careers, these individuals have consistently come to the aid of Hong Kong and the world, to address infectious diseases threats such as seasonal influenza, H5N1, Sars, Mers, Ebola and now Covid-19. They represent the best.”

Poon is currently the head of the school’s division of public health laboratory sciences, and Peiris is the chair professor in virology. Both have been actively at the forefront of the research on Covid-19, and helped design the coronavirus detection tests, used in public health labs in dozens of countries and territories.

Fukuda also warned that social media could be “hostile and misleading”, calling on his colleagues to be “thoughtful and sober” if they were approached by others to give information.

On Monday, Yan, who said she fled to the United States for her own safety, gave a second interview on Fox News in which she claimed she was waiting to tell the US government what she knew, adding she feared for her life.

She had earlier accused HKU of failing to act on her findings that Chinese authorities were aware of human-to-human coronavirus transmission in late December.

Yan described herself as one of the world’s first scientists to study the new virus from the end of December, when her supervisor Poon had asked her to secretly investigate developments in mainland China.

She then obtained on December 31 what she called first-hand information from a scientist friend working for the Chinese Centre for Disease Control and Prevention, who claimed there was human-to-human transmission because of the existence of clusters within families. Poon had told her to keep her findings under wraps, she said.

Checks by the Post showed that HKU microbiologist Professor Yuen Kwok-yung had notified Hong Kong health minister Sophia Chan Siu-chee of the outbreak in Wuhan on December 31, noting its pandemic potential and its similarity to severe acute respiratory syndrome (Sars), which could spread among humans.

That same day, the Centre for Health Protection in Hong Kong announced for the first time that it was monitoring a cluster of pneumonia cases in Wuhan, believed to be the source of the original outbreak, in response to a report from the mainland’s National Health Commission. The report had said the virus was not contagious among humans.

Beijing only confirmed human-to-human transmission on January 20, when the country’s leading infectious disease expert Zhong Nanshan acknowledged the phenomenon in an interview with state media CCTV.

On December 31, Poon was quoted by media as saying there was still no evidence to determine if the atypical pneumonia cases found in Wuhan were related to Sars.

“It will be very important to actually find out the aetiology of this disease,” Poon told local media at the time, referring to the causes of the illness. “Having atypical pneumonia means we don’t know the pathogens responsible for this disease at the moment. So we need to look for that and try to exclude Sars or other types of coronaviruses.”

A search on PubMed, an authoritative database of life sciences and biomedical research, showed Yan was involved as a co-author in two studies linked to Covid-19. One was about the viral load of the pathogen, published in The Lancet Infectious Diseases Journal on March 19 this year. The other was a study on the transmission of Covid-19 in golden hamsters, published in Nature in May.

A short introduction of Yan on Virtual Keystone Symposia, which hosts online scientific talks, states that her research interests include infectious diseases while her recent work focused on universal influenza vaccines.

HKU issued a rebuttal of Yan’s claims late on Saturday, arguing the contents of her interview had no scientific basis and resembled hearsay. It did not say when and why Yan left the university.

“Specifically, Dr Yan never conducted any research on human-to-human transmission of the novel coronavirus at HKU between December 2019 and January 2020, her central assertion of the said interview,” the university statement said.