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n expensive screening program designed to keep the Zika virus out of the Red Cross’ blood supply has caught fewer than a dozen infected donations, a new study published Wednesday revealed.

The program, which costs roughly $137 million a year to operate, detected only eight units that tested positive for the virus between June 2016 and September 2017. And half of those units contained Zika antibodies as well as virus, which suggests they probably would not have been able to infect a recipient, if anyone had been transfused with them.

The high screening cost and low number of positive detections works out to about $5.3 million for each positive unit the Red Cross pulled from the system, said the study, published in the New England Journal of Medicine.

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The current policy, set by the Food and Drug Administration, requires the Red Cross and other blood suppliers to test each donation they receive individually, which accounts for the high cost.

The blood system operators would like to be able to dial back that screening, though they aren’t advocating doing away with it altogether — even though Zika transmission appears to be at very low levels in the Americas these days.

Dr. Susan Stramer, senior author of the study and vice president of scientific affairs at the American Red Cross Biomedical Services, said that moving to test blood donations in small pools as opposed to individually would cut the cost of Zika screening in half. And it would bring Zika screening in line with the way the Red Cross and others test for the variety of pathogens they look for in blood donations, including HIV, West Nile virus, and hepatitis B and C.

“For Zika, we treat that virus differently than we treat any other virus,” Stramer told STAT. “So I think the argument we’re trying to make is that Zika should be treated just like West Nile or HIV … etc., and not have to test each donation individually. Because it’s certainly a waste of resources and a waste of our capacity, which we should be using that for other things.”

An expert group that advises the FDA on blood safety issues looked at the issue in a meeting last December and recommended that the blood supply operators be allowed to revert to pooled testing for Zika. But to date, the FDA hasn’t authorized the change.

“Certainly if it’s something related to increased safety, FDA would act very quickly. But in this case they haven’t acted as quickly as we would have liked,” Stramer said.

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In an emailed statement, the FDA said the agency does not typically comment on individual studies. It did not indicate why the agency has not yet acted on its advisory panel’s recommendation from December, but said that it is considering on a revision of its Zika screening guidelines.

A commentary published by the journal noted that rescinding or scaling back a blood screening program is harder to do than putting one in place. Dr. Evan Bloch, a pathologist and transfusion medicine specialist at Johns Hopkins School of Medicine, noted that there had never been a decision to stop screening for a pathogen.

Bloch and Stramer both noted that it’s not clear what the future holds when it comes to Zika. Transmission could flare up again, increasing the risk to the blood supply.

“When I initially started writing the paper, I really thought: ‘Yes, this is a stupid policy.’ I was very kind of black and white about it,” Bloch said in an interview. He admitted, though, that as he explored the pros and cons, his views moderated. “I began to realize that if you were transported back to like the early ’80s with HIV, had they been this aggressive in their response, you might have had a very different outcome with HIV and the blood supply.”

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