Two researchers are proposing genetic experiments on the H7N9 flu virus to see what would happen if it could spread from person to person.

An outbreak of H7N9 bird flu with pandemic potential has some researchers calling for controversial experiments to help countries prepare for the worst. Others say not so fast.

A pair of letters jointly published today in the journals Science and Nature represent the researchers’ views and a response by officials at the U.S. Centers for Disease Control and Prevention (CDC), the National Institutes of Health (NIH), and the U.S. Department of Health and Human Services (HHS).

The researchers, Ron A.M. Fouchier of Erasmus Medical Center in the Netherlands and Yoshihiro Kawaoka of the University of Wisconsin-Madison, both virologists, argue the H7N9 virus already contains mutations and could spread among humans. Patients being treated for the illness have also developed resistance to some medications, they wrote.

A report published Tuesday in the British Medical Journalshowed the first evidence of person to person transmission of H7N9, though the authors said its ability to spread is “limited and non-sustainable.”

Fouchier and Kawaoka want to undertake tests called “gain of function” experiments, in which the virus would intentionally be mutated further to see what would happen if it were able to travel from person to person. The experiments are necessary to prepare for a public health crisis, the researchers argue.

“We hope that by being transparent, people will realize the value of what we do and feel less anxious about this research,” Kawaoka told Healthline.

“The H7N9 virus has several mutations that were also found in flu viruses that caused pandemics in the last century,” Fouchier told Healthline. “It also has some mutations that are associated with airborne transmission.”

The virus emerged less than six months ago in China. So far, there have been 134 confirmed cases and 43 deaths, according to the World Health Organization. Most people who have been infected got the virus at live chicken markets.

The response letter, signed by representatives of public health agencies, calls for extra oversight in conducting these gain of function experiments. The HHS said it will require an additional level of review before funding the studies. The CDC also tightened biosafety regulations for experiments on the H7N9 virus.

Many in the medical community believe gain of function tests are risky because mutated viruses could be passed along to a scientist and then spread to the general population. Others worry that if such research is published, it could put the key to developing a deadly virus in the wrong hands.

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said he has ongoing concerns about the experiments. “There’s one group that believes this work can and should be done with pretty much minimal oversight, and another group that believes it shouldn’t be done at all,” he told Healthline. “I’m in between.”

Although he believes the research could provide some new and important information, Osterholm said the U.S. government needs to be vigilant. “We just haven’t done an extensive risk-benefit analysis. Is there really a benefit?”

Gain of function research has been done on the H5N1 flu virus as well. Osterholm said the experiments have not succeeded in letting scientists measure the ongoing risks of transmission, which is one of the benefits the researchers are touting.

Dr. Michael Shaw, associate director for laboratory science in the CDC’s influenza division told Healthline that gain of function experiments present a “tremendous ethical dilemma,” but in the end most scientists and public health officials believe they are needed. “It’s the intersection of science, politics and ethics, with potentially huge ramifications.”

Kawaoka said the experiments do not pose an ethical problem for him because they’re in the interest of public health. The experiments must be approved by his Institutional Bioethics Committee, which usually includes public input. He is also waiting on the go-ahead from his funding sources.

“For viruses, gain of function can mean that one makes a dangerous virus potentially more dangerous. Some people argue that that is too risky,” his co-author Fouchier added. “However, in virology research we have specially designed laboratories available at different biosafety levels, and numerous additional risk mitigation measures to reduce risks to the absolute minimum.”