Should the United States keep screening all blood donations for Zika?

Before the coronavirus pandemic, the Zika virus dominated headlines as the mosquito-transmitted disease spread across the Americas and Southeast Asia in 2015.

In 2016, as evidence emerged that Zika could be transmitted by blood transfusion, the U.S. Food and Drug Administration (FDA) ordered that all blood donations be screened with a newly developed nucleic acid test for the virus.

Now, as the COVID-19 crisis begins to ease, an analysis published in the Annals of Internal Medicine reexamines whether Zika screening is still warranted.

On balance, the researchers say the answer is likely no. “When looking at how an end to screening might affect the serious complications about which the FDA is rightfully concerned, a model from our lab found greater than 99% certainty that the United States should expect fewer than one case every thousand years,” said Margaret Brandeau, professor of management science and engineering and, by courtesy, of medicine at Stanford University. “That is an extremely low risk to be spending millions annually to prevent,” added Brandeau, whose lab has developed influential model-based health policy analyses on bioterror defense, HIV treatment and the opioid epidemic.

Zika screening was implemented with unprecedented haste, and prevented any transfusion-transmitted cases from occurring. The global epidemic ended in 2016, and testing has identified no Zika-positive donations since March 2018. In 2019, America’s Blood Centers, which represents donation sites in more than 600 communities, urged the FDA to consider halting Zika testing, allowing blood centers to redeploy the roughly $80 million a year they now spend “to protect against future threats.” The FDA may have been poised to do just that at an April 2020 meeting of the Blood Products Advisory Committee, which has purview over testing requirements, but that meeting was canceled as the coronavirus pandemic leapt to the forefront.

The United States is the only country to implement universal screening for Zika virus, and no clinical disease from transfusion-transmitted Zika has been recorded worldwide. Although Zika fever is typically a mild illness, infection can cause serious complications. About one in thirty thousand infections cause Guillain-Barré syndrome, a neurological disorder that can cause permanent paralysis. Transmission from mother to fetus can cause congenital Zika syndrome, a pattern of devastating birth defects that often include small head size and brain damage.

These serious complications, and particularly the risk of birth defects, have loomed large in the FDA’s reasoning about safety measures, as has the possibility for a large Zika resurgence. Mosquito-transmitted diseases can have a volatile epidemiology, changing considerably from one year to the next.

However, the study finds that a much larger outbreak than seen in the U.S. to date would be needed for the rate of serious complications to exceed once-in-a-decade levels. This is unlikely while large swaths of the population in the tropical areas most favorable for Zika virus retain immune experience that reduces susceptibility. A prior study also found that Zika surveillance models can monitor the risk of new outbreaks. Travel-based donor deferral or Zika testing can be deployed in a targeted fashion should a resurgence occur.

Ironically, the coronavirus crisis that derailed the FDA’s last attempt to revisit the Zika requirement may prompt a renewed look at the burdens placed on blood centers, which have struggled to maintain a sufficient blood supply while facing new social distancing policies. The Annals study provides evidence that, busy as the agency has been, the time may be right to reconsider its current policy.

“If the FDA decided that it could prudently remove the Zika screening requirement, that would free up resources blood centers could redeploy toward the many other challenges they are facing,” Brandeau said.

Alton Russell authored the paper “Estimating the effect of discontinuing universal screening of donated blood for Zika virus in the 50 U.S. states” while a graduate student in the Brandeau lab, in conjunction with his dissertation, “Models to inform the safe collection and transfusion of donated blood”.