A team of experts tasked by the World Health Organization (WHO) to investigate the origin of SARS-CoV-2 has ruled out the possibility that the virus that causes  the Covid-19 originated from a laboratory leak in the Chinese city of Wuhan.

The development was announced on February 9, during a media briefing on Covid-19 origin in which the team presented its initial findings.

The press briefing was held from Wuhan.

The Covid-19 pandemic has infected over 106 million people and killed over 2.3 million of them worldwide, according to data from Johns Hopkins University.

WHO says that the pandemic shows the devastating impact emerging zoonotic diseases – those that can be transmitted from animals to humans – can have on societies.

The joint international team comprised 17 Chinese experts and 17 international experts from 10 other countries, including Denmark, Netherlands, Australia, US and UK.

The team also includes five WHO experts; two Food and Agriculture Organization (FAO) representatives and two representatives of the World Organization for Animal Health (OIE).

Some people have held a controversial theory that the virus may have leaked from a laboratory.

But, Peter Ben Embarek, the head of the WHO mission, said it was "extremely unlikely" that the virus that has caused the pandemic which has wreaked havoc worldwide, leaked from the laboratory.

The studies considered four hypotheses.

They include the possibility of direct transmission of the virus from an original animal to human; and introduction of the virus through an intermediary species such as an animal potentially closer to human. 

Others are possible virus transmission through the food chain in particular, with frozen food acting as the surface for the transmission of the virus into the human population; and the possibility of a laboratory related incidence.

"We took a systematic approach to look at all these hypotheses, putting arguments for and against, and assessing the likelihood using a standardised set of parameters,” he said.

"Our initial findings suggest that the introduction to an intermediary host species is the most likely pathway and the one that will need more studies and more specific targeted research,” he said.

 "However, the findings suggest that the laboratory incidence hypothesis is extremely unlikely to explain the introduction of the virus into the human population,” he said.

"And therefore, it is not a hypothesis that implies to suggest future studies to support our future work into understanding the origin of the virus, he pointed out.

The hypothesis of direct spillover from an original animal source into the human population is also a possible pathway and is also generating recommendation for future studies, he indicated.

Meanwhile, he said they did not find evidence of large outbreaks that could be related to the cases of Covid-19 before December 2019 in Wuhan or elsewhere.

Prof. Liang Wannian, head of China's Health Commission, said evidence from surveys and tactic studies so far have shown that coronaviruses most highly related to SARS-CoV-2 are to be found in bats and pangolins, suggesting these mammals may be the reservoirs of the virus that causes Covid-19, on the basis of high similarity in sequences between the sampled viruses and SARS-CoV-2.

"However, the viruses identified so far from neither of these species are sufficiently similar to SARS-CoV-2 to serve as direct progenitor of SARS-CoV-2,” Wannian said in Chinese, through an English interpreter.