The US government has lifted a ban on making lethal viruses in the lab after ruling that the benefits of the research outweigh the risks.

Researchers will now be able to manufacture strains of influenza, Sars and Middle East Respiratory Syndrome (Mers) in the lab.

The decision overturns a three-year research funding ban imposed after safety breaches at federal institutions risked the outbreak of dangerous viruses. In 2014 it was feared around 75 workers at the US Centers for Disease Control and Prevention (CDC) were exposed to anthrax bacteria and are receiving treatment. Later that year, vials of smallpox which had been left in a cardboard box were found by a government scientist at a research centre near Washington.

A subsequent ban covered federal funding for any new so-called "gain-of-function" experiments that enhance pathogens.

One of the concerns with "gain-of-function" research is that while the work may produce useful insights, laboratory-enhanced pathogens could be used for biowarfare or bioterrorism if they fell into the wrong hands.