Spread of Zika slows in Florida
State health official report says ‘herd immunity’ has led to a decline in the virus
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 — likely has contributed to Zika’s decline outside the continental United States, said Dr. Henry Walke, incident manager for Zika response with the U.S. Centers for Disease Control and Prevention (CDC).
“People that were infected before can’t be infected again. That’s our understanding,” Walke said in a Miami Herald report. “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 the United States. 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,” said Florida Department of Health spokesperson Mara Gambineri.
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.
By the end of 2016, state health officials had confirmed 1,456 Zika infections, including 285 cases spread by mosquitoes in Miami and Miami Beach.
The infections caused the CDC to issue an unprecedented domestic travel advisory warning pregnant women to avoid Miami-Dade County because the virus can cause severe birth defects.
There is no vaccine or treatment for the virus, which can also spread through sexual contact.
Florida health officials have reported 384 pregnant women who tested positive for Zika since January 2016, with nine delivering children with Zika-related birth defects.
So far this year, Florida health officials have reported a total of 135 Zika cases, but none have been linked to mosquitoes in the state. The CDC lifted its travel warning for Miami-Dade County in June.
But experts warn residents and visitors not to feel complacent about contracting the virus.
“The threat is still there,” Walke said. “It hasn’t gone away. It will not go away anytime soon.”
Frequent rainfall, which benefits breeding mosquitoes, and the fact that many people infected with Zika don’t feel any symptoms — such as fever, joint pain, red eyes or a rash — can fuel an outbreak in spite of increased mosquito-control efforts, said Bill Petrie, the county’s new mosquito control director.