'Herd immunity' may be curbing U.S. Zika numbers

The number of Zika infections has dropped dramatically in Florida this summer, and scientists say herd immunity may be the reason why.

In practical terms, herd immunity means that people traveling to the United States from South America and the Caribbean may have been infected with Zika in the past, but they can no longer pass the virus on to mosquitoes that might pass it on to local residents.

"If a large enough proportion of the herd — be it cows or mice or people — are resistant to a disease, it's very difficult for the disease to spread," said Uriel Kitron. He is chair of the department of environmental sciences at Emory University, in Atlanta. He is also a faculty member in the PBEE program.

Kitron, who studies Zika in Brazil, said that very few Zika infections have been seen there since a major outbreak occurred in that country back in 2015.

"We think a large proportion of the people have been infected, many of them without symptoms, and have lifelong immunity. There has been very little transmission since," he said.

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