New research published in the journal Nature Microbiology has found the number of Zika infections in the current epidemic should peak at around 93 million people in Latin America and the Caribbean, including 1.6 million childbearing women.

In the news release, the study team said their calculations represent a worst-case scenario.

“In other words, we think these projections may be pretty good for a location where Zika shows up and starts an epidemic, but at the same time we acknowledge that due simply to random chance and the fact that some places are relatively isolated and sparsely populated, the virus won’t make it to every single corner of the continent,” said study author Alex Perkins, an assistant professor of biological sciences at the University of Norte Dame.

Perkins added that the figures laid out in the study represent infections, not clinical cases. Many people infection with the Zika virus do not show symptoms.

“Only about 20 percent of people who are infected develop any symptoms whatsoever, and even fewer than that will seek medical care and show up in government statistics,” he said.

Modeling using Herd Immunity

In the study, the research team looked at a concept called “herd immunity,” which is when so many people become immune to a contagion, an epidemic cannot sustain itself.

“This idea was very central to our approach, as was the idea that more people become infected before herd immunity can extinguish an epidemic in areas where mosquitoes are plentiful and transmission is very intense,” Perkins said.

The researchers said a primary objective of their study was to establish concrete estimates of how big the Zika epidemic might become.

“Although there is lots of uncertainty around our projections and we will have a better idea of the situation as we get more data, our projections are some of the very first to give a ballpark estimate of the total number of people who might be at risk,” Perkins said. “Even after several months of intense research and analysis of this epidemic, our projection is some of the only information that decision makers have to go by right now.”

The study wasn’t based on data from the present epidemic. Rather, it used data from past dengue and chikungunya fever epidemics.

“In this research, we were interested in seeing what we could come up with at the earliest stages of the epidemic before we had the luxury of lots of data to work with,” Perkins said. “By the time we have enough data to make forecasts based on traditional approaches, much of the damage has already been done by the epidemic and it is too late for the research to be actionable.”

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