Herd immunity slows spread of Zika

MIAMI — 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, probably 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.”

However, experts warn that herd immunity elsewhere won’t stop the virus from re-emerging in this country. That has happened in Florida with other mosquito-borne viruses in recent years.

“As we’ve seen with chikungunya and dengue, it is not unlikely that we will experience small outbreaks of Zika in the future,” Florida Department of Health spokeswoman Mara Gambineri said in a written statement.

Also, herd immunity eventually wears off, said Derek Cummings, an epidemiologist with the University of Florida’s Emerging Pathogens Institute.

“As years go by, more people are born into a population and they haven’t encountered Zika, and so they’re going to introduce susceptibility into the population,” Cummings said. “Some number of years from now, those susceptible populations will rise to where you’d have sufficient numbers and then maybe we’d be doing this all over again.”

This year, Florida health officials have reported 135 Zika cases, but none has been linked to mosquitoes in the state. The CDC lifted its travel warning for Miami-Dade County in June.