Infectious Diseases

Updated 14 July 2016

Zika epidemic should fizzle out within three years: study

The outbreak of the Zika virus is likely to have peaked and the epidemic should be over within a few years, say researchers.

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The outbreak of the mosquito-borne Zika virus, blamed for a surge in birth defects, has likely reached its peak in Latin America and the epidemic should be over within three years, researchers said Thursday.

The study by scientists at Imperial College London appears in the US journal Science.

"The current explosive epidemic will burn itself out due to a phenomenon called herd immunity," said Neil Ferguson, a professor at Imperial's School of Public Health.

"Because the virus is unable to infect the same person twice -- thanks to the immune system generating antibodies to kill it -- the epidemic reaches a stage where there are too few people left to infect for transmission to be sustained."

This should happen within two to three years, he added.

Then, this herd immunity "will likely delay the next large Zika epidemic for more than a decade."

The virus, though first discovered in 1947, largely took public health officials by surprise when it began spreading through the Americas last year and causing birth defects.

The rise in infants born with irreversible malformations has been most acute in Brazil, where some 7 438 suspected microcephaly cases have been reported as of May and 1 326 cases confirmed, the study found.

Typically, Brazil saw fewer than 200 annual cases of microcephaly -- in which the infant is born with an unusually small head and brain.

Zika infections have been reported in dozens of countries throughout the Caribbean and Latin America.

The United States has seen a rise in travel-associated cases, but so far no local transmission has been observed.

Vaccine too late?

Ferguson also warned that efforts to slow the spread of Zika, by increasing mosquito-control measures, could actually prolong the epidemic.

And efforts underway to design a vaccine -- which officials have said could take several years -- may come to fruition too late, he said.

"If our projections are correct, cases will have dropped substantially by the end of next year, if not sooner," said Ferguson.

"This means by the time we have vaccines ready to be tested, there may not be enough cases of Zika in the community to test if the vaccine works."

Amid concerns about the potential spread of Zika during the upcoming Olympic Games in Rio de Janeiro, a separate report out Wednesday by the US Centers for Disease Control and Prevention said that the risk of transmission is low.

Read more: Low Zika impact expected at Rio Olympics

As many as 500 000 international visitors and athletes from 207 countries are expected to travel to Rio, but "this travel volume represents a very small fraction -- less than 0.25 percent -- of the total estimated 2015 travel volume to Zika-affected countries," said the CDC.

"Visitors to the Games are expected to have a low probability of mosquito-borne Zika infections because the Games will occur during the winter season in Rio de Janeiro (August 5-21 and September 7-18, respectively) when the cooler and drier weather typically reduces mosquito populations."

The US agency did raise particular concern, however, about Chad, Djibouti, Eritrea and Yemen. It said "these four countries do not have substantial travel to any country with local Zika virus transmission, except for their participation in the Games, and have environmental conditions and population susceptibility to sustain mosquito-borne transmission of Zika virus."

Pregnant women should not travel to the Olympics, and all visitors should take steps to avoid mosquito bites and prevent potential sexual transmission of the virus, the CDC urged.

Read more:

Zika virus: pregnant women shouldn't travel to Brazil

Surge of Brazilian babies born with small heads

Zika may also cause stillbirth