Zika virus epidemic to last 'another three years'

“Zika epidemic to last another three years as ‘too late’ to control it, say researchers,” reports the Telegraph Online.

A team of researchers at Imperial College London aimed to explore the dynamics of the current Zika epidemic in Latin America and used this data to calculate the potential future spread of the virus.

From the analysis in the study, the main predictions were that the current Zika epidemic will largely be over in three years, with seasonal variations based on mosquito populations.

Additionally, once the current epidemic is over, there will be a delay of at least a decade before any more large epidemics of Zika virus. This is because a large percentage of the population will be immune to infection – known as herd immunity.

However, the researchers highlighted the importance of developing new vaccines and testing potential interventions to prevent another epidemic, or at least, contain it quicker than the current outbreak.

As with all modelling studies the results are based on data available and some assumptions. Therefore, it’s important to keep in mind the uncertainty that comes with predicting potential future trends of disease.

Where did the story come from?

The study was carried out by researchers from Imperial College London and one from Johns Hopkins University in the US. It was funded by the Medical Research Council, the Bill & Melinda Gates Foundation, the National Institutes of Health, and the UK NIHR Health Protection Research Unit in Modelling Methodology at Imperial College London.

The study was published in the peer-reviewed journal: Science. It is available on an open-access basis, meaning it’s free to read online.

Media coverage of this study was widespread and varied. The Telegraph Online reported that “attempts to control the outbreak are now pointless because authorities have missed the chance to prevent the disease exploding,” which is not the case.

BBC News was more accurate with its reporting, taking into account that “predicting anything with any degree of certainty was impossible”.

What kind of research was this?

This was a modelling study that aimed to explore the trends of the current Zika epidemic and use this data to predict the potential spread of the virus.

Zika virus is a disease mainly spread by mosquitoes, it doesn’t naturally occur in the UK. Originally discovered in 1947, the virus received little attention until the 2015 outbreak in Brazil.

Modelling studies such as this help policy makers get an idea of what the potential public health impact of a disease might be. For example, helping them to plan ahead or assist with making recommendations about the control of the disease.

What did the research involve?

The researchers obtained publicly available surveillance data on weekly suspected and laboratory-confirmed Zika cases in Brazil during the 2015-16 outbreak. They used this data to demonstrate the dynamics of the current epidemic and explore how the Zika infection may evolve.

To do this, they used the estimates of “the average number of secondary infections” and “the time between sequential rounds of infection,” to calculate the potential future spread of the Zika virus.

In addition, they explored the potential impact of human mobility and the changing age groups which will be affected in the future as immunity develops.

What were the basic results?

The researchers made a number of predictions based on their model.

The headline prediction is that the current epidemic will largely be over in three years, with seasonal variations based on mosquito population. Once the current epidemic is over, herd immunity will lead to a delay of at least a decade before other large epidemics occur.

The average age of infection is predicted to fall in future epidemics, as older people will be more likely to be immune to the Zika virus through past exposure. However, the analysis suggests the risk to pregnant women is unlikely to change.

Although it’s difficult to predict the timing of the rounds of epidemics, the analysis suggests future epidemics of Zika virus will typically last for less than six months.

How did the researchers interpret the results?

The researchers concluded the Zika virus is “like Ebola, a public health crisis in which policymakers have had to make decisions in the presence of enormous uncertainty”.

However, they recommended that the government response to Zika virus should not mirror Ebola as ”Zika and Ebola epidemiology and thus policy options differ fundamentally.”

They suggested that the current epidemic “is not containable” and “at best, interventions can mitigate its health impacts”.

Despite the warning, they concluded that the current Zika epidemic will run its course naturally, eventually providing “a multiyear window to develop new interventions before further large-scale outbreaks occur.”

Conclusion

This modelling study aimed to explore the trends of the current Zika epidemic and use this data to predict the future spread of the virus.

From the analysis, the main predictions were that the current epidemic will largely be over in three years, with seasonal variation based on mosquito populations. Additionally, once the current epidemic is over, there will be a delay of at least a decade before another large Zika virus epidemic.

However, as the researchers acknowledge, with any modelling study the results are based on data available and some assumptions. There is a great deal of uncertainty that comes with predicting potential future trends of disease.

For example, it’s difficult to foresee climate change or predict how preventative interventions, mosquito control, or population behaviour may affect their predictions.

Additionally, this analysis was only able to look at trends in Latin America. This means the predictions may not be applicable to other parts of the world, such as Asia, and the figures represent estimates, rather than exact numbers.

Links To The Headlines

Zika epidemic to last another three years as ‘too late’ to control it, say researchers. The Daily Telegraph, July 14, 2016

Zika epidemic will end in three years, study suggests. BBC News, July 14 2016

Zika epidemic could burn itself out in three years as people become immune say experts. Mirror Online, July 14 2016

Is the Zika epidemic nearly over? Disease to burn out in the next 2 years because it ‘will have run out of people to infect’. Mail Online, July 15 2016

Zika epidemic has peaked and may run its course within 18 months, say experts. The Guardian, July 14 2016

Links To Science

Ferguson NM, Cucunuba ZM, Dorigatti I, et al. Countering Zika in Latin America. Science. Published online July 14 2016