Most members of a Food and Drug Administration advisory committee considered that data support maintaining current testing protocols for Zika virus in the blood donor pool. However, committee discussion entertained the idea of revisiting testing strategies after another year or 2 of Zika virus epidemiological data are available.
In its last guidance regarding Zika virus testing, issued in July 2018, the FDA recommended that either minipool nucleic acid testing (MP NAT) or individual donor (ID) NAT be used to screen for Zika virus. Current guidance still requires conversion to all-ID NAT “when certain threshold conditions are met that indicate an increased risk of suspected mosquito-borne transmission in a defined geographic collection area.”
In the first of three separate votes, 11 of 15 voting members of the FDA’s Blood Products Advisory Committee (BPAC) answered in the affirmative to the question of whether available data support continuing the status quo for Zika testing. Committee members then were asked to weigh whether current data support scaling back to a regional testing strategy targeting at-risk areas. Here, six committee members answered in the affirmative, and nine in the negative.
Just one committee member, F. Blaine Hollinger, MD, voted in favor of the third option, elimination of all Zika virus testing without reintroducing donor screening for risk factors in risk-free areas pending another outbreak in the United States. Dr. Hollinger is a professor of virology and microbiology at Baylor College of Medicine, Houston.
The committee as whole wasn’t swayed by a line of questioning put forward by chairman Richard Kaufman, MD. “I will be the devil’s advocate a little bit: We learned that there have been zero confirmed positives from blood donors for the past year. Would anyone be comfortable with just stopping screening of donors?” asked Dr. Kaufman, medical director of the adult transfusion service at Brigham and Women’s Hospital, Boston.
A wide-ranging morning of presentations put data regarding historical trends and current global Zika hot spots in front of the committee. Current upticks in infection rates in northwest Mexico and in some states in India were areas of concern, given North American travel patterns, noted speaker Marc Fisher, MD, of the Center for Disease Control and Prevention’s Arboviral Disease Branch (Fort Collins, Colo.) “We’re going to see sporadic outbreaks; it’s hard to predict the future,” he said. “The new outbreak in India raises concerns.”
Briefing information from the FDA explained that Zika virus local transmission peaked in the United States in late summer of 2016. More than 5,000 cases were reported in the United States and over 36,000 in Puerto Rico. This has plummeted to 220 in 2018, with about two-thirds of these cases occurring in the territories, mostly (97%) from Puerto Rico across all 3 years.
Zika viremic blood donors dropped by an order of magnitude yearly, totaling 363 in 2016, 38 in 2017, and just 3 in 2018. Of the 363 detected in 2016, 96% came from Puerto Rico or Florida, noted Dr. Fisher.
The number of suspected and confirmed cases in the Americas overall has also dropped from over 650,000 in 2016 to under 30,000 in 2018, with most cases in 2018 being suspected rather than laboratory confirmed. In contrast to testing conducted in North America, few cases in much of Central and South America were laboratory confirmed.
Asymptomatic infections have occurred in blood donors, said the FDA, with 1.8% of blood donations in Puerto Rico testing positive for Zika virus during the peak of the outbreak. Transmission by transfusion is thought to have occurred in Brazil.
Although Zika virus infections have plummeted in the United States and worldwide, prevalence and rates of local transmission are unpredictable, said the FDA, which pointed to sporadic increases in autochthonous transmission of viruses such as dengue and chikungunya that are carried by the same mosquito vector as Zika.
Some of the committee’s discussion centered around finding a way to carve out protection for those most harmed by Zika virus – pregnant women and their fetuses. Martin Schreiber, MD, professor of surgery at Oregon Health and Sciences University, Portland, proposed a point-of-care testing strategy in which only blood destined for pregnant women would be tested for Zika virus. Dr. Schreiber, a trauma surgeon, put forward the rationale that Zika virus causes harm almost exclusively to fetuses, except for rare cases of Guillain-Barré syndrome.
In response, Dr. Kaufman pointed out that with rare exceptions for some bacterial testing, all testing is done from samples taken at the point of donation. The supply chain for donor blood is not set up to accommodate point-of-care testing, he said.
Answering questions about another targeted strategy – maintaining a separate, Zika-tested supply of blood for pregnant women – Susan Stramer, PhD, vice president of scientific affairs for the American Red Cross, said, “Most hospitals do not want, and are very adamant against, carrying a dual inventory.”
Ultimately, the committee’s discussion swung toward the realization that it may be too soon after the recent spike in U.S. Zika cases to plot the best course for ongoing testing strategies. “We are at the tail end of a waning epidemic. ... I think it would probably be a pretty easy question for the committee and for the agency if we actually had some way of having a crystal ball and knowing that the current trend was likely to continue,” said Roger Lewis, MD, PhD, professor at the University of California, Los Angeles, and chair of the department of emergency medicine at Harbor-UCLA Medical Center.
“I think that is not the question,” he went on. “I think the question is, What is the optimal strategy if we have no idea if that tail is going to continue in this current trend. ... And that maybe the committee ought to be thinking about what is the right strategy for the next 2 years – with an underlying assumption that this is a question that can be brought back as we learn more about how this disease behaves.”
The FDA usually follows the recommendations of its advisory committees.