The World Health Organization will continue pushing until it finds an answer to how the Covid-19 pandemic started, the agency's chief said Wednesday following a report suggesting it had abandoned the search.

Solving the mystery of where the SARS CoV-2 virus came from and how it began spreading among humans is considered vital for averting future pandemics.

Yet an article on the Nature website Tuesday said faced with a lack of cooperation from China, where the outbreak began in late 2019, the WHO had given up on the search.

"We need to continue to push until we get the answer," agency chief Tedros Adhanom Ghebreyesus told reporters, referring to the search for the origins of the virus.

"Knowing how this pandemic started is very, very important and very crucial," he said.

He said he had recently sent a letter to a top official in China "asking for cooperation, because we need cooperation and transparency in the information... in order to know how this started."

The two main theories that have been hotly debated have centered on the virus naturally spilling over from bats to an intermediary animal and into humans or escaping due to a lab accident.

The Nature report suggested that the WHO has "quietly shelved the second phase of its much-anticipated scientific investigation into the origins of the Covid-19 pandemic".

It quoted Maria Van Kerkhove, the WHO expert leading the agency's Covid response, saying that "there is no phase two".

The WHO planned for work to be done in phases, she told the report, but "that plan has changed", adding that "The politics across the world of this really hampered progress on understanding the origins".

Van Kerkhove responded angrily Wednesday when asked about the article, attributing the interpretation that WHO had shelved its origins search to "an error in reporting, which is really quite concerning because it's causing some headlines that are inaccurate".

"WHO has not abandoned studying the origins of Covid-19, we have not and we will not," she said.

"There was no quiet shelving of plans and we have been, and we continue to be open, transparent."

The WHO carried out a first phase of investigation by sending a team of international experts to Wuhan, China, in early 2021 to produce a first phase report, written in conjunction with their Chinese counterparts.

But that investigation faced criticism for lacking transparency and access, and for not sufficiently evaluating the lab-leak theory, which it deemed "extremely unlikely".

The political rhetoric reached fever-pitch over that theory, which was favored by the administration of former US president Donald Trump but always flatly rejected by China.

Tedros has meanwhile from the start insisted that all hypotheses remained on the table, and the WHO has repeatedly called on China to provide further access to investigate.

While the initial plan had been to send a second team, Van Kerkhove recalled Wednesday that the WHO had shifted tactics in mid-2021, deciding instead to create a team of scientists with an expanded scope to investigate new pathogens and study how to prevent future pandemics, while continuing to probe Covid-19's origins.

The Scientific Advisory Group for the Origins of Novel Pathogens (SAGO) was created "to conduct an independent assessment of the origins of Covid-19, but also to work more broadly to establish a framework to understand the origins of any future epidemic and pandemic pathogen, and the origins in which it emerges," Van Kerkhove said.

"We will continue to ask for countries to depoliticize this work, but we need cooperation from our colleagues in China to advance this," she said.

Tedros said there were two reasons for not abandoning the origins search.

The first was scientific, he said: "We need to know how this started in order to prevent the next one."

"The second (is) moral: millions of people lost their lives, and many suffered, and the whole world was taken hostage by a virus."

"It's morally very important to know how we lost our loved ones."

(AFP)

WHO Director-General Tedros Adhanom Ghebreyesus. (AP)

WHO chief to 'push until we get the answer' on Covid origins