From AP/US News and World Report August 12th 2017
MIAMI (AP) — The waning of Zika outbreaks in the Caribbean and South America has helped slow the spread of the mosquito-borne virus in Florida this year, according to health officials.
Herd immunity, when enough people in an area are infected with a virus and develop resistance to it, likely has contributed to Zika’s decline outside the continental United States, Dr. Henry Walke, the U.S. Centers for Disease Control and Prevention’s incident manager for Zika response, said in a Miami Herald report .
“People that were infected before can’t be infected again. That’s our understanding,” Walke said. “So you don’t have as much of the virus circulating. That’s true not only in Puerto Rico but throughout the Caribbean and throughout South America.”