A researcher who created one of the H5N1 mutants and a leading U.S. health official say the threat has been blown out of proportion, offering what they said were clarifications and “new data” to better gauge the risk it presents.

Contrary to widespread reports, the researcher, Ron Fouchier of Erasmus MC in Rotterdam, the Netherlands, revealed that the virus made in his lab does not kill ferrets infected by the aerosol route. And it is more difficult to transmit the virus than Fouchier previously described.

Fouchier criticized press accounts that suggested, as he put it, that “this virus would spread like wildfire if it would come out of our facility.” Not only did the mutant fail to spread 100% of the time, he said, animals infected via the aerosol route were not as likely to transmit the virus as ferrets infected with seasonal influenza strains that routinely spread between humans: They made copies of the virus more slowly, and the peak levels of virus were much lower.

“We have to conclude that this virus does not spread yet like a pandemic or seasonal influenza virus,” Fouchier said, in contrast to what he reportedly said in Malta. He did not respond to Science‘s request to discuss this discrepancy.

Fouchier further contended that if H5N1 does acquire mutations that make it more transmissible in humans, it likely will not cause severe disease in most people. To date, H5N1 has killed nearly 60% of the confirmed cases, but he said he did not think this fatality rate was accurate, because many cases that do not cause serious illness probably go undetected.

Science contacted seven of the 23 NSABB members, and although several promised to review revised manuscripts with an open mind, they all said the new information and the clarifications presented at the ASM discussion, at first blush, did not change their views.

See also: H5N1 influenza virus research to continue, says WHO

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