The Zika virus scare that sparked unprecedented travel warnings and a rush on bug spray in 2016 has petered out in its second year, with scientists saying that efforts to stamp out disease-carrying mosquitoes and the human immunity built up over the last year have combined to contain the spread.
Where the U.S. recorded roughly 225 mosquito bite-related Zika cases last year, so far just one case has been reported this year — a Texan, infected in a county bordering Mexico.
And while more than 2,000 people had contracted the disease while traveling outside the U.S. at this point in 2016, that’s fallen to just 200 travel-related cases this year, the Centers for Disease Control and Prevention said.
Experts say cases are down across the hemisphere as people have built up antibodies over the last two years and are better able to resist infection. Most people who contract Zika don’t show symptoms anyway, so even those who weren’t sure if they were infected will be part of the population’s natural shield against transmission.
“Zika epidemics, in a way, act like a vaccine. Once enough inhabitants of a country or community are infected, they develop immunity,” said Lawrence O. Gostin, a law professor at Georgetown University. ” At a certain point it then becomes much harder for the disease to spread because there is a similar kind of herd immunity that one would expect from a vaccine.”
The World Health Organization’s trend data show a massive spike in Zika in the Americas in early 2016, with 25,000 to 40,000 cases recorded each week in South America, mainly in Brazil. Case counts steadily leveled off, dipping below 5,000 in the final weeks of 2016 and to a few hundred cases per week about halfway through 2017.
“When we see a virus sweep through countries like that, in the years following introduction of the virus, we tend to see a decline in cases as more people in the first year were exposed,” CDC spokesman Tom Skinner said.
It’s a far cry from the dire warnings in 2016 that suggested the disease could spread across the Southern U.S., and could be a threat for years to come.
Public health professionals scrambled, and Washington nearly lurched into a government shutdown showdown, with President Barack Obama and fellow Democrats demanding billions of dollars in new Zika-fighting cash.
Zika was a relatively obscure virus before it hopscotched to the Americas and burst into the headlines early last year, when scientists found an unprecedented link between an insect-borne disease and birth defects. The most recognizable one is microcephaly, in which infants have abnormally small heads.
A government report this year said women with suspected cases of Zika had a 5 percent rate of virus-spawned birth defects, while those with lab-confirmed cases showed a 10 percent defect rate.
U.S. health officials said they remain on watch, particularly in the areas that showed local transmission last year.
“We wouldn’t be surprised to still see some localized transition of the virus like we’ve seen in South Texas and like we could see in southern Florida,” Mr. Skinner said. “It’s unpredictable. I can’t sit here and say we’re going to have ‘this many’ cases.”
But with fewer people bringing the virus back with them to the U.S., it lessens the risk of people being bitten by infected mosquitoes here.
“Given Zika in Florida is mostly introduced from the Caribbean, Zika may not be a problem in Florida in 2017, although it could reoccur in the out years,” said Peter J. Hotez, dean of the National School of Tropical Medicine at the Baylor College of Medicine in Houston.
Scientists said the dearth of local cases could also be attributable to public awareness campaigns and efforts to eradicate the Aedes aegypti mosquito that typically carries Zika.
Florida has yet to report a single case of local transmission this year despite being the epicenter for localized transmission last year, when it recorded more than 200 cases that largely stemmed from outbreaks in the artsy Wynwood neighborhood of Miami and a stretch of Miami Beach.
Florida had reported 30 of those cases as of this point last year.
Texas, meanwhile, reported about a half-dozen cases later in the year in the Brownsville area near the Mexican border.
Now the Lone Star State accounts for the only documented case by mosquito bite within the continental U.S. in 2017 — a person in Hidalgo County whose infection came to light in late July.
“We’ve had a lot fewer travel cases related to Central America and the Caribbean. However, reports of local transmission in Mexico have been moving northward, so that’s our primary concern now,” said Chris Van Deusen, spokesman for the Texas Department of State Health Services.
Puerto Rico, a U.S. territory, was swamped with locally transmitted Zika last year — 35,000 cases in all — but it has reported only 550 cases to the CDC so far this year. The island’s health ministry declared the epidemic over in early June as case counts slowed to a crawl.
The Caribbean region overall showed a similar trend line, topping out at about 10,000 cases per week toward the middle of 2016 before dwindling to less than 300 per week by mid-2017, according to the Pan-American Health Organization.
Some trouble spots remain in Mexico, while countries that didn’t face the brunt of the outbreak in 2016, such as Ecuador and Peru, saw a spike in cases earlier this year. But at a rate of hundreds of cases per week, it was far less than the height of the outbreak in hard-hit countries like Brazil, so for now it is unlikely to pose a grave risk of travel-related Zika in the U.S.
After last year’s spending fight in Congress, lawmakers ended up funding $1.1 billion in anti-Zika money.
Mr. Skinner said the U.S. was “able to do a lot with that money,” including $50 million to Florida, to detect and track the disease, though the supplemental funding has all been spent or will run out at the end of the fiscal year in September.
Demand for federal funding has shrunk with the case counts — at least for now.
“At this time, Florida has not requested any additional funds, but we are prepared to do so should it be needed,” Florida Health Department spokeswoman Mara Gambineri said.
President Trump’s fiscal 2018 budget does not request Zika-specific dollars from Congress, though the Office of Management and Budget says states are free to tap into related funding sources, such as public health grants or the CDC’s vector-borne disease program, as necessary.
The budget request also includes $500 million for a CDC block grant that would allow states to spend money on their most pressing challenges, the budget office said.