Results from a controversial research project in which scientists created a pandemic strain of the deadly H5N1 bird flu virus in the lab were finally published on Thursday, after an eight-month delay while scientists and biosecurity officials debated how much of the information should be made public.

Scientists wanted to know what changes in the H5N1 virus, which cannot currently spread between people, were necessary for it to become transmissible through the air via coughs and sneezes. They genetically modified the wild H5N1 virus and found that it would only require mutations at five locations in its genome for a pandemic strain to emerge.

Ron Fouchier, professor of molecular virology in the department of virology at the Erasmus Medical Center in the Netherlands, led the team of scientists who created the virus. They genetically altered the wild H5N1 virus at three locations and then used it to infect ferrets – the standard model used to mimic flu in humans. As the virus spread between the animals by physical contact, it picked up additional mutations until, with only five mutations to differentiate it from the wild virus, it became airborne and able to spread via the kind of tiny droplets produced in a cough or sneeze.

The results of Fouchier's experiment are published today in Science.

Last month, Yoshihiro Kawaoka at the University of Wisconsin-Madison published details of another form of the bird flu virus that can pass between people, which was created by merging a mutated strain with the swine flu virus that sparked a human pandemic in 2009.

The publication of both Kawaoka and Fouchier's research had been delayed by several months after the US government's National Science Advisory Board for Biosecurity (NSABB) warned that the information should be censored to avoid being misused, for example by terrorists. Scientists argued that the research should be published in full so that they and public health authorities would be prepared with vaccines and public health protocols if the wild strain of H5N1 naturally mutated into a form that could easily spread between people.

Bird flu was first identified in poultry around 16 years ago and, in the rare instances when it infects people, can cause serious illness or death. It cannot currently spread between humans, but scientists wanted to find out how many genetic changes it would take for the virus to become airborne.

"Our main conclusion is that the H5N1 bird flu virus can acquire the ability of aerosol transmission between mammals, and we show that as little as five mutations, but certainly less than 10, are sufficient to make H5N1 virus airborne," said Prof Fouchier. When the virus had become airborne, however, it did not kill the infected ferrets.

Scientists had thought that, to start a pandemic, flu viruses would first have had to mix their genes with another virus in the animal host. But Fouchier's work showed that this "reassortment" process was not required for H5N1 to become airborne.

In an accompanying study in Science, Derek Smith, professor of infectious disease informatics at the University of Cambridge, used computer and mathematical models to work out whether the types of virus created by Fouchier and Kawaoka could ever occur naturally. Smith's team analysed surveillance data on avian H5N1 viruses from the past 15 years and found that two of the required five mutations from the modified viruses had already occurred in existing strains.

His team also showed that it was possible for a virus to evolve the three remaining mutations in a single host. Evolving four or five extra mutations would be more difficult but Smith was unable to quantify that risk. "We now know that we're living on a fault line," said Smith. "What we have discovered in this working collaboration with Drs. Fouchier and Kawaoka is that it's an active fault line."

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, said the benefits of publishing the results of Fouchier's and Kawaoka's work outweighed the risks. "When you get out something into the general literature, you stimulate thoughts and input from people who at first glance you may not think would have an interest in it. So when it's out there in the general literature, anyone from x-ray crystallographers to structural biologists to physiologists to viral epidemiologists can get involved."

• This article was amended on 22 June 2012. The original referred to ferrets as rodents. This has been corrected.