The world’s largest public health authority has weighed in with the most authoritative statement yet on the use of Crispr to alter the DNA of human babies. Eight months after a rogue Chinese scientist revealed he had secretly created the world’s first gene-edited children, the World Health Organization is asking countries to put a stop to any experiments that would lead to the births of more gene-edited humans. On Friday, the WHO’s director-general put out a statement urging “that regulatory authorities in all countries should not allow any further work in this area until its implications have been properly considered.”

While stopping short of the all-out moratorium that many scientists called for in the hours and days after Chinese scientist He Jiankui revealed his controversial work in November, the WHO’s position is a strong rebuke of He’s work. But whether it will prove a powerful deterrent to any who would hope to follow in his footsteps remains to be seen.

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“I commend the WHO for taking a stance on what I think is the right side of the issue,” says Fyodor Urnov, a gene-editing scientist at the Altius Institute for Biomedical Sciences in Seattle and the University of California, Berkeley. (In 2015, Urnov coauthored a perspective in Nature titled Don’t Edit the Human Germ­line.) He believes the technology is not just premature but medically unnecessary. “So the more firm stance we have across health authorities the better. And this is as clear a stance as one could possibly take. But it’s only talking about people operating within established regulatory frameworks, and by definition this cannot address what a rogue actor can do.”

Human germline editing is already effectively banned in the US, because of a law preventing the US Food and Drug Administration from even reviewing clinical trial applica­tions involving genetically modified human embryos. But in Russia, at least one scientist has started to make plans to begin testing Crispr in IVF clinics to prevent inherited deafness. And because Crispr components, unlike enriched plutonium, can be easily acquired over the internet for research purposes, there’s little the WHO can do to curb unscrupulous scientists from conscripting IVF physicians into creating underground embryo-editing clinics. But for aboveboard efforts to test gene editing at the embryo level, the WHO’s stance could come as a real blow.

Megan Molteni covers DNA technologies, medicine, and genetic privacy for WIRED.

“While it doesn’t necessarily carry the weight of law, the WHO has some interesting powers,” says Carolyn Brokowski, a research associate and bioethicist at Yale Medical School, who has studied the more than 60 ethics reports and statements issued by the international community on human germline editing since 2015. “Given the uncertainty at this time, it would be unfortunate for any country or institution to do anything that’s contraindicated by the WHO. Overall, I expect it to put a damper on enthusiasm for moving forward with this technology.”

The recommendation comes from the WHO’s 18-member expert advisory committee on human genome editing, which it formed in December. The committee delivered this judgment at a meeting in Geneva in March, along with a suggestion that the WHO create a transparent global registry for all experiments related to human genome editing. Currently, more than 20 clinical trials around the world are using a different, less controversial type of editing that involves altering the DNA in so-called somatic cells (things like white blood cells and bone marrow cells, rather than sperm or eggs). Just this week, two gene-editing companies in the US announced they were beginning to enroll and treat patients for the first time. Editas Medicine has teamed up with Allergen to treat a form of inherited blindness by injecting Crispr components into patients’ eyes. And as NPR reported Monday, Crispr Therapeutics and Vertex have begun infusing billions of Crispr-edited cells into sickle cell patients in Nashville.