Photo: Joern Pollex (Getty Images)

A new study published Thursday in the New England Journal of Medicine reveals that it took more than $40 million over a 15-month period to screen nearly every blood donation sent to the American Red Cross for the mosquitoborne Zika virus. The report found that the massive effort—which went into effect following Zika outbreaks that reached as far as Florida in 2016—might be not worth keeping up anymore.

Three years ago, the rapid emergence of Zika in the Americas—and its devastating ability to cause birth defects in children born to infected mothers—set off a global health crisis. In response, US health agencies not only warned people against traveling to areas where Zika became endemic, like Brazil, but recommended that blood donation organizations screen certain donations for the virus.

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The American Red Cross, which is responsible for about 41 percent of all stateside donations, took this advice to heart. Starting in June 2016, it first screened pooled donations from states where Zika transmission from mosquitos was at risk of becoming local, like Florida. Specifically, it looked for Zika RNA in blood using nucleic acid testing (NAT). But following another FDA recommendation in August 2016 that universal screening should be the standard, it switched to testing every individual donation.

The researchers behind this study, which include Red Cross scientists, looked at 4.3 million screened donations made from June 2016 to September 2017. Nine percent of these donations were included in the pooled samples, none of which tested positive for Zika. Of the remaining 3.9 million donations, 160 were initially flagged for Zika, but only nine donors were subsequently confirmed to be positive.

At least two cases of Zika have been spread through infected donated plasma, but it’s tough to say how infectious the people who tested positive for Zika may have actually been, the authors added.

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Based on the costs—$6 for tests of the pooled blood, and $10 for the individual tests—they estimated it took $41.7 million to perform Zika screening. Over a year’s time, that means it took $5.3 million to track down a single case. And if the same math were applied to all blood donations collected in the US, the annual cost of screening for Zika would amount to $137 million, the study concluded.

The findings come on the heels of an ongoing debate over the future of Zika screening. This December, the FDA was advised by a committee of experts on blood safety to scale back its screening strategy—a recommendation the study authors and Red Cross are now also endorsing.

“With these data, the Red Cross supports transitioning to mini-pool NAT for Zika virus in U.S. areas that are not experiencing local outbreaks. Specifically, that means the Red Cross would continue to test every unit of donated blood from across the country during the entire year for evidence of the virus using mini-pool NAT,” senior study author and vice president of Scientific Affairs at the American Red Cross Susan Stramer said in a statement to Gizmodo. “In areas undergoing local transmission, testing would immediately convert to individual donation NAT.”

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Such a screening policy would mirror the one already in place for diseases like West Nile Virus, believed to be the most common mosquitoborne disease in the US. And it would likely cut the cost of annual Zika screening in half.

The threat of Zika, while still real, has definitely waned since the first burst of outbreaks from 2015 to 2016. There were over 40,000 known cases of Zika in the US in 2016 (most infections cause no symptoms, or cause illness that resembles the flu in adults). These were mostly in Puerto Rico, where local mosquito transmission became widespread. But by 2017, there were just 1,000 known cases. And so far in 2018, there have only been 68 cases. The NEJM authors also noted that just one blood donation out of more than six million collected by the Red Cross since September 2017 to February 2018 has tested positive for Zika.

Few if any blood safety experts have argued that the move to universally screen for Zika was a waste of time and resources, given how little we knew about the virus back then (though there are still plenty of mysteries remaining). If anything, an accompanying editorial in the NEJM points out, it’s the sort of move that might have saved untold lives in a different era.

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“The initial decision to test for ZIKV should not be condemned; a similar proactive response to HIV could have resulted in a reality very different from the pandemic that unfolded in the 1980s,” the editorial’s authors, led by Evan Bloch of the John Hopkins School of Medicine, wrote.

For the time being, the FDA still hasn’t changed its stance on universal Zika screening, nor has the Red Cross stopped screening every individual donation. It would be an unprecedented move: The US has never scaled back on any screening policy, only occasionally changing the tests meant to be used.

“We appreciate the uncertainty following the emergence of Zika virus in 2015 and 2016, and remain committed to continuously monitoring for Zika virus activity and taking proactive actions to safeguard the blood supply when necessary,” Stamer said.

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[NEJM]