July 17, 2016

Study predicts Zika epidemic will end in three years because about 90% of the people in effected areas will have already had Zika

The current Zika epidemic is likely to end within three years because there will be too few people left to infect, a team of scientists is predicting. Herd immunity against infectious disease requires that 80-95% of the entire population are immune.

Writing in the journal Science, they said this could lead to a gap of 10 years before the next epidemic.

The Imperial College London team created a model using data from the current outbreak in Latin America.

But a Zika expert said predicting anything with any degree of certainty was impossible.

The scientists, from the Medical Research Council Centre for Outbreak Analysis and Modelling at Imperial, calculated that the epidemic, which began in Brazil in 2015, would burn itself out within three years.

Science - Countering Zika in Latin America

Because the virus is unable to infect the same person twice, as more and more people become infected, reaching a level called "herd immunity", infection levels fall and the epidemic dies out.

Until there was a new generation who had not been exposed to Zika virus, there would be a long period with few new cases, the researchers said.

They said this mirrored the pattern of other epidemics, such as chikungunia - a virus similar to Zika.

Earlier this year, the World Health Organization declared the Zika virus a global public health emergency because of the risk to newborn children.

Although Zika infection is largely mild, with most people having no symptoms, it is known to cause microcephaly - babies born with undersized heads.

In severe cases, children can die and babies who survive can face intellectual disability and developmental delays.

The Olympic Games are going ahead in Rio, Brazil, in August, despite recent concerns from leading scientists that holding the event is "unethical".

The research paper said the current outbreak was not "containable" and targeting the Aedes aegypti mosquito carrying the virus would have limited impact.

Prof Neil Ferguson, lead author of the research, said that any efforts to slow the spread of the virus could actually prolong the current epidemic.

"Slowing transmission between people means the population will take longer to reach the level of herd immunity needed for transmission to stop.

Ferguson is saying to give up on the current outbreak and use the preparation for the next generation when more new people would be vulnerable to it.


As evidence grew for a causal link between Zika infection and microcephaly and other serious congenital anomalies
(1), the World Health Organization (WHO) declared the Latin American Zika epidemic a public health emergency of international concern in February 2016
(2). The speed of spread has made effective public health responses challenging. Immediate responses have included vector control
(3) and advice to delay pregnancy in a few countries
(4), followed by an extended recommendation to all affected countries by WHO in June 2016. These have merits but are likely to have limited effectiveness
(5) and may interact antagonistically. Fuller understanding of dynamics and drivers of the epidemic is needed to assess longer-term risks to prioritize interventions.

SOURCES - BBC News, Journal Science,

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