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Zika Disappears

Almost as quickly as it emerged as a public health threat a few years ago, Zika has receded from headlines and legislative agendas as the number of new cases crashes to a small fraction of what they were.

The Centers for Disease Control and Prevention has identified only seven cases of Zika acquired through local, mosquito-borne transmission in the United States proper for all of 2017. There were 661 such cases in U.S. territories, mostly Puerto Rico, but that still represents a startling decline from 36,367 cases in U.S. territories the year before.

Last summer, the journal Science examined this sharp drop in Zika cases, which was already evident by midyear. That article noted that cases were also plummeting in Latin America and other parts of the Caribbean. Brazil, the country most severely affected, had 205,578 probable Zika cases in 2016, but only 13,253 cases had been reported by mid-2017.

This change has not arrived because of some dramatic scientific breakthrough. There is still no Zika vaccine on the market, despite the urgency to develop one when the epidemic was at its peak. In fact, the reasons for the unexpected remission are unclear. But it is probably a combination of factors including basic mosquito control measures, more elaborate steps including the use of drones and artificially sterilized insects to control the spread of the virus, and a concept known as “herd immunity:” Some scientists think that enough people have been exposed to Zika (which usually produces either undetectable or mild symptoms, despite the devastating consequences in pregnancy) to develop antibodies that prevent reinfection and further transmission. Much of the population in areas affected by Zika is potentially now immune to the current strain.

Whatever the reason, we certainly can’t credit the emergency funding that Congress approved late in 2016 after much political posturing. Cases have dropped dramatically all over the Americas, notably including the epidemic’s epicenter in Brazil. Our Congress had nothing to do with that.

The decline of Zika is great news on a societal level, but of course it does nothing to alleviate the misery of individual children and families who are affected. They are still out there, and they will need all sorts of support for many years. Many won’t get much due to poverty and government dysfunction in their Latin American homelands. But even here in the United States, Zika had a noticeable impact on the statistics for birth defects – most apparent in Puerto Rico, though hurricane devastation has far eclipsed Zika as an overall source of misery on the island.

Summer is upon us. In the humid states along the Gulf and southern Atlantic coastlines, this is prime mosquito season. Scientists and statisticians will keep a close eye on any indications that Zika is making a resurgence. It doesn’t seem likely, but then again, nothing about this epidemic has been predictable.

It is still unclear whether a Zika vaccine will clear clinical trials and be released to the market any time soon. The Pharmaceutical Journal reported in February that the World Health Organization is tracking about 45 vaccine candidates from various sources. While most are still in preclinical development, some have reached clinical trials, and a few have made it to phase II. (Vaccines approved by the Food and Drug Administration typically go through three phases of clinical trials before approval, though many continue to phase IV after that point as well.) But there is still a lot researchers admit they do not know about how the virus spreads or why it has appeared to stop.

Lyle Petersen, the head of CDC’s vector-borne disease division in Fort Collins, Colorado, told Science that declining transmission complicates vaccine trials, as there are fewer ways to see if the vaccine effectively halts the disease’s spread. Diminished fear and diminished funding also makes a vaccine less of a priority – something we could still come to regret if Zika re-emerges as a major threat. It’s a tough call. Do we keep pouring resources into fighting a disease that seems to be curing itself? Are we willing to spend scarce public health dollars on a gamble that Zika will turn out to be anything worse than, say West Nile, which generates far more headlines than its general health consequences deserve?

For now, let’s take good news where we can find it, without forgetting about the real victims of the Zika outbreak. For the past few years, I avoided sending staffers of childbearing age (male and female) to Brazil, where we have clients, in order to protect their families’ health. I am more open to such business travel now. In South Florida, where I live, mosquito repellant remains a good idea, but that is always the case in our rainy summers. Still, I see no reason to stress about dining outside at one of our many waterfront restaurants.

And we should try to keep politics out of our public health discussions as much as we can. Amid presidential election politics two years ago, Zika funding got caught up in extraneous issues like funding for Planned Parenthood. It delayed any action to the point that the action was largely irrelevant by the time it arrived. We caught a break with this epidemic, which seems to have decided to cure itself. We might not be so lucky next time.

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