A group of prominent scientists and others are calling for a limit to experiments that modify influenza and other dangerous viruses to make them spread more easily in mammals.

Three recent safety lapses in federal labs with smallpox, anthrax, and avian influenza are a reminder of the “fallibility” of even the most secure labs, writes a group calling itself the Cambridge Working Group in a July 14 statement drafted at Harvard University. “Laboratory creation of highly transmissible, novel strains of dangerous viruses, especially but not limited to influenza, poses substantially increased risks” that an accidental infection could lead to a global outbreak, they write.

The group urges that experiments that produce potential pandemic strains “should be curtailed until there has been a quantitative, objective and credible assessment” of the risks, potential benefits, and alternatives. They call for a process akin to Asilomar, a 1975 summit that came up with guidelines for recombinant DNA technology.

Concerns about “gain-of-function” experiments with influenza erupted in 2011 after two teams genetically tweaked the H5N1 avian flu virus, which has killed some people, to make it more transmissible in mammals. Supporters of such studies say knowing which mutations help the virus spread in humans is useful for surveillance efforts and developing pandemic vaccines. After much debate and a moratorium on the H5N1 studies, a consensus emerged that the experiments could resume with new safeguards.