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The World Health Organization on Tuesday fine-tuned its advice on measures people should take to prevent the sexual transmission of the Zika virus, adopting a more cautious approach.

The global health agency said it now recommends that people who have traveled to places where Zika is spreading should not try to conceive a child for six months after their return, regardless of whether they have had symptoms of the illness.


Previously, women who had traveled to places with Zika spread were urged to wait eight weeks before trying to conceive. The agency also recommended that men who traveled to areas where the virus was spreading wait only eight weeks after their return, as long as they didn’t experience signs of illness. (Men who had traveled to those areas and had shown signs of Zika were urged to wait six months.)

Recent reports have shown that women with Zika virus can infect their sex partners and that sexual transmission can occur even if the infected person isn’t experiencing Zika symptoms. It is estimated that 4 out of every 5 people who contract Zika have such a mild infection that they show no signs of illness.

Dr. Nathalie Broutet, a WHO expert on sexually transmitted infections, said the new advice simplifies the message — though she acknowledged remembering the advice may be easier than abiding by it.


Broutet said the experts who updated the recommendations looked at recent reports from Europe of men whose semen tested positive for fragments of Zika virus six months after their infection.

But they decided they didn’t need to lengthen the time during which precautions should be taken. Broutet said the longest interval recorded from infection of a man to sexual transmission to his partner is 41 days. And detecting fragments of virus doesn’t mean there are whole, infectious viruses in semen.

“Six months is a reasonable time frame between what we know and the data that we have and what is feasible,” she told STAT.

The new WHO recommendations are more conservative than the advice issued by Centers for Disease Control and Prevention on preventing sexual transmission of Zika.

The CDC urges men who have had symptoms of Zika infection to practice safe sex or abstinence for six months to prevent sexual transmission of the virus. But women who’ve had symptoms need only wait eight week before trying to become pregnant, the agency says. And men and women who may have contracted the disease during travel but who had no symptoms are also advised to take precautions during an eight-week period after their return.

The WHO also used the new guidance to try to clear up confusion caused when it issued the previous iteration of the advice, in early June. Unclear wording created the impression the agency was urging people who live in places where Zika is spreading to delay having children, and was widely reported in the media as such. But that was not the intent, the WHO later said.

The new guidance says that sexually active people who live in places where Zika is spreading should be counseled and offered “a full range of contraceptive methods” so they can make an informed choice about whether and when to become pregnant in order to prevent Zika-induced birth defects and other adverse events in pregnancy.