US researchers have developed a new lethal Covid strain in a laboratory – echoing the type of experiments many fear started the pandemic.

The mutant variant — which is a hybrid of Omicron and the original Wuhan virus — killed 80 percent of mice infected with it at Boston University.

When a similar group of rodents were exposed to the standard Omicron strain, however, they all survived and only experienced 'mild' symptoms.

The scientists also infected human cells with the hybrid variant and found it was five times more infectious than Omicron.

This suggests the man-made virus might be the most contagious form yet.

It will no doubt surprise many Americans that such experiments continue to go on in the US despite concerns similar studies may have led to the global Covid outbreak.