A US lab has been accused of "playing with fire" after creating a hybrid super-Covid that killed 80% of the mice tested on.
Boston University scientists combined the most dangerous element of Omicron with the original virus strain which emerged in Wuhan in late 2019. Such gain-of-function research is thought to be a potential reason behind the pandemic itself.
It aims to improve the ability of a pathogen to cause disease in an effort to increase preparedness.
However, it can also put people at risk of contracting it inadvertently.
Some experts have said such research should be forbidden and authorities who gave the green light should be held to account.
Professor Shmuel Shapira, a leading scientist in the Israeli Government, told MailOnline : "This should be totally forbidden, it's playing with fire."
Dr Richard Ebright, a chemist at Rutgers University in New Brunswick, New Jersey, said: "If we are to avoid a next lab-generated pandemic, it is imperative that oversight of enhanced potential pandemic pathogen research be strengthened."
According to reports, researchers from Boston and Florida combined Omicron's spike protein with the original Covid-19 mutation.
Omicron's spike has dozens of mutations, making it highly infectious.
When a group of mice were exposed to standard Omicron, they all survived and only experienced 'mild' symptoms.
However, 80% of those exposed to the hybrid strain perished.
While the spike protein is responsible for infectivity, changes to other parts of its structure determine its ability to inflict mortality, researchers said.
Dr Ebright continued that the new ePPP research is "especially concerning" considering the previous US government green-lit on chimeric SARS-related coronaviruses at Wuhan Institute of Virology that "appears not to have undergone the prior risk-benefit review".
He said to avoid lab-generated pandemics it is "imperative" that such oversights "be strengthened" and that government agencies behind them "be held accountable".
It comes as the number of Covid-19 deaths registered in England and Wales is rising again, new figures suggest.
Some 400 deaths registered in the seven days to October 7 mentioned coronavirus on the death certificate, according to the Office for National Statistics ( ONS ).
This is up 39% from 287 deaths in the previous seven days, and is the highest weekly total since late August.
It is the first signal that the current wave of infections is likely to be driving an increase in deaths involving Covid-19 - though numbers have yet to match those seen during this year's summer wave.
Death registrations peaked at 810 in the week to July 29, following the surge in infections caused by the BA.4 and BA.5 Omicron subvariants of Covid-19.
This peak was well below the level seen during the Alpha wave in January 2021, when weekly deaths reached nearly 8,500.
