More scientists have fought back the allegation that SARS-CoV-2, the virus that caused the COVID-19 pandemic, leaked from a lab.

On a TV show on June 14, U.S. comedian and former TV host Jon Stewart claimed the COVID-19 pandemic was started by an accidental lab leak. His remarks were condemned by Dr Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine and co-director of the Texas Children's Hospital Center for Vaccine Development, as reported by The Independent on June 16.

"Right now, the reality is there is no smoking gun to say that it's of laboratory origin," Hotez told TMZ Live, urging Stewart and others to be more prudent when discussing the potential origin of COVID-19.

"They're putting the entertainment value of this above what's reality," said Hotez. "It causes a lot of damage because a number of scientists who work on coronaviruses including myself feel that we're under attack right now."

In contrast, scientists still believe a natural origin is the most possible way.

"The animal origins pathway of COVID-19 is still the most logical," Dominic Dwyer, an Australian medical virologist in the World Health Organization's COVID-19 origin-tracing joint study with China, said in an op-ed published in The Guardian on Friday.

"Based on nearly all emerging human viruses of the last 50 years (including SARS in 2003 and MERS in 2012), animals are the likely source," said Dwyer. "By virtue of their ecology, bats play a special role, not just with coronaviruses, but with Ebola, Hendra and others."

The virologist refuted the lab leak theories, as before a leak, "the virus must be present in the laboratory already and there would have to be a breakdown of usual regulated laboratory procedures around sample collection and preparation. For further spread, the infected worker must transmit the virus to close contacts and through them to the wider community," all of which have not been currently supported by any clear evidence.

Moreover, RaTG13, a bat virus found by researchers at the Wuhan Institute of Virology that is 96 percent identical to SARS-CoV-2 at the genome level, "is only a genetic sequence and has not been grown in the laboratory."

Read more: Here's how scientists know the coronavirus came from bats and wasn't made in a lab

He noted that the lab leak theories, ranging from accidental to deliberate and even state-sponsored, "are easy claims to make, comprehensible to everyone, part of popular culture and catering to political discourse."

Seeking the origin of the novel coronavirus is "not for the sake of reproach, but to guide preparations for the next time around," stressed Dwyer.

Rinat Maksyutov, director general of Russia's State Research Center of Virology and Biotechnology Vector, also stressed that experts have no doubt in the natural origin of the novel coronavirus, TASS news agency reported on June 17.

Maksyutov said that the changes in the novel coronavirus amount to 20 percent compared to the previous coronavirus, adding, "To create such a virus artificially would be impossible."