The government Tuesday lifted a three-year moratorium on funding for research into ways that certain viruses can be made more virulent and transmissible, announcing a new plan for assessing applications to study these and other dangerous pathogens.

The new policy for pathogens capable of creating a pandemic will allow researchers who want to study them to apply for funding through the new process outlined by the Department of Health and Human Services.

The end of the moratorium applies to research on the SARS, MERS, influenza and other dangerous viruses. The October 2014 pause was put in place after researchers in Wisconsin and the Netherlands sparked a debate by announcing in 2011 that they had made the deadly H5N1 bird flu virus more contagious in ferrets, which are used as a model for how disease might spread among humans. This kind of research is known as "gain of function" because it introduces new abilities into existing germs.

Shortly before the ban, the Centers for Disease Control and Prevention acknowledged that lab workers had been exposed to anthrax and that a lethal avian flu virus had been sent to a lab that had asked for a less deadly strain.

In a briefing for reporters Monday, Francis Collins, director of the National Institutes of Health, the main government funder for biological research, estimated that only a "handful" of facilities would qualify to conduct this kind of research, which is generally aimed at understanding how viruses mutate and developing vaccines.

"This kind of research can only be conducted in a very few places that have the highest level of containment," Collins said.

Collins also disclosed that during the moratorium, 10 of the 21 research efforts that had been stopped obtained waivers to resume their work. Those waivers applied to five MERS and five flu experiments, he said.

With the new policy in place, the government is able to lift the moratorium, Collins said. The new policy for "potential pandemic pathogens" would apply to the three viruses and others that researchers may want to investigate, such as Ebola. New requirements include that the potential risks of the research be justified by the potential benefits; that there is no other feasible way to answer the same question that poses less risk; and that the proposed experiment be reviewed by an independent expert panel.

"This is a way of regularizing a rigorous process that we really want to make sure we are doing right," Collins said.

Other pathogens are covered under the government's policy for Dual Use Research of Concern, which covers life sciences research that, if misused, might threaten public health, national security and the environment.

Beth Cameron, vice president for global biological policy and programs at the nonprofit Nuclear Threat Initiative, called having a plan in place "a step in the right direction." But she emphasized that safety would still depend largely on strong security measures at each lab to protect against an accidental release and govern who is allowed to work on the experiments.

Mitigating risk requires "knowing what you're doing, why you're doing it, what the benefits of the research are," she said. "And it means understanding the risk to the public while you're doing it."

Still, Cameron said, the United States now becomes what she thinks may be the only nation in the world with such a plan, which highlights the need for international discussion of this issue.

She said she is concerned about the "increased ability to use tools in order to create viruses and bacteria that can evade countermeasures."

Andrew C. Weber, a former assistant secretary of defense for nuclear, chemical and biological defense programs during the Obama administration, said the new criteria are strict enough that "it is difficult to imagine any research proposal that would meet these sensible criteria." He says the new policy should make it difficult to get approval for gain-of-function research. "The risks to the public of deliberately enhancing pandemic pathogens are too grave to justify the modest potential benefits."

Read more:

Decades old smallpox vials found in NIH storage room

About 75 CDC scientists exposed to anthrax

CDC chief admits mishandling of anthrax, other pathogens