What Happened to the Zika Epidemic?

The Real Truth About Vaccines

Jun 28, 2026

Do you remember the Zika virus?

“In March 2015, Brazil reported a large outbreak of rash illness, soon identified as Zika virus infection and, in July 2015, found to be associated with Guillain-Barré syndrome.”
Zika virus disease outbreak 2015-2016

Do you remember the epidemic it triggered?

Over the course of 2016, the virus spread to at least 58 countries and territories; outbreaks occurred in Puerto Rico, the U.S. Virgin Islands, American Samoa, Florida and Texas, and pregnant women infected with the disease during travel were identified in 44 states. Last year in the U.S., 77 Zika babies died in the womb, while 51 babies were born with Zika-related birth defects. Each of the surviving children will cost an estimated $10 million to care for during their lifetimes.
As Zika Season Nears, States Brace for an End to CDC Funding

An epidemic that started in 2014, hit 92 countries and territories, caused congenital birth defects, and peaked in 2016.

What Happened to the Zika Epidemic?

An epidemic that hasn’t returned, even though we still don’t have a Zika vaccine…

So how was the Zika epidemic brought under control, and how has it been kept at bay without a vaccine?

No, it wasn’t that everyone started taking ivermectin…

“In early 2016, WHO declared Zika virus-related microcephaly and other neurological disorders a Public Health Emergency of International Concern. By that time, the virus had caused an estimated 750 000 infections in the Americas. The name congenital Zika syndrome was coined to identify children with severe, specific manifestations of congenital Zika virus infection, including: severe microcephaly with partly collapsed skull; thin cerebral cortices with subcortical calcifications; macular scarring and focal pigmentary retinal mottling; congenital contractures; and marked early hypertonia.”
A decade later, what have we learned from the Zika epidemic in children with intrauterine exposure?

One reason, of course, is that a lot of people got sick with Zika and built up immunity to the virus.

“Most experts say the sharp decline in Zika cases is due, at least in part, to herd immunity. When enough people become immune to a virus, whether through vaccination or natural immunity, then that disease can't easily travel from person to person.”
Why did Zika disappear?

That’s right, herd immunity is not just about vaccines.

“Our analysis suggests that once the current epidemic is over, herd immunity will lead to a delay of at least a decade before large epidemics may recur.”
Countering the Zika epidemic in Latin America

There is a big problem with this kind of natural herd immunity though - it doesn’t last, as everyone who is born after the epidemic won’t have any immunity and that will eventually trigger another outbreak. In fact, those are the same epidemic cycles that we saw in the pre-vaccine era.

Besides herd immunity, there are other likely other reasons that Zika hasn’t returned.

“By July, 2017, Zika virus cases had dropped considerably in Brazil, which was concurrent with a rise in the number of Chikungunya cases. The shorter incubation period in the mosquito vector and declining temperatures during autumn favoured the rise of Chikungunya cases over Zika virus in endemic settings. This observation suggests that other arboviruses can eventually outcompete Zika virus in endemic areas.”
A decade later, what have we learned from the Zika epidemic in children with intrauterine exposure?

Interestingly, it is actually thought that other viruses can outcompete Zika virus.

Plus, interventions to control the mosquitoes that transmit the Zika virus to us likely helped a little.

Will Zika Return?

What else should people know about the Zika virus?

“The ZIKV pandemic has waned, but the virus still poses a public health threat, as shown by continued reports of outbreaks in Asia, India, and Africa. Although at present we do not have the tools to predict where and when the next large epidemic will happen, the large numbers of susceptible persons residing in aedes-infested regions make a reemergence of ZIKV likely.”

Zika isn’t gone.

“Many of the shuttered USAID programs have been working to address disease outbreaks in their home countries, improving the health of the people who live there, and limiting risks to travelers. For example, the US government, in collaboration with private donors (such as the Gates Foundation in the US, Wellcome Trust in the UK, and the Oswaldo Cruz Foundation [Fiocruz] in Brazil) supported efforts by the World Mosquito Program to combat dengue, Zika, and chikungunya viruses in Latin America by targeting the mosquito that transmits these viruses, and achieved striking success.”
The Domestic Consequences of Defunding Global Health

And the measures taken by Donald Trump and RFK, Jr. to dismantle our public health systems will likely help Zika return, including that they reduced funding and staff for international outbreak detection.

There are Zika cases in many countries, although not on the scale of the last epidemic.

Plus they cut USAID funding for mosquito control programs that help combat Zika!

What Happened to a Zika Vaccine?

Considering the scope of the last Zika epidemic, it should be no surprise that a Zika vaccine had been in development.

So what happened?

“Many hurdles remain, however, before a vaccine will become available. The limited number of cases occurring globally limits the ability of studies to evaluate the protective effects of vaccines in phase 3 human trials.”
Progress toward discovery of Zika virus vaccines and therapeutics

Not enough cases happened…

“Multiple vaccines, including inactivated, live-attenuated, DNA, mRNA, virus-vectored, and recombinant peptides, have progressed to clinical studies while there are also others at different development stages.”
An updated review of Zika virus vaccine development

While it is very good that there aren’t a lot of people getting sick with Zika, it does mean that there aren’t enough people for Zika vaccine trials. After all, you can’t test if a vaccine is effective if they can’t be exposed.

Bottom line - because of funding cuts to public health, we won’t be ready for the next Zika epidemic.

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