Emergencies

Potential use of the polio surveillance system for the detection of Zika virus outbreaks

23 January

Zika has challenged outbreak surveillance systems in many at-risk, low-resource countries. WHO is, therefore, exploring every avenue to detect people with Zika and related neurological complications in a cost-effective way. One of the avenues may be to use the existing infrastructure for surveillance of polio.

What is the link between Zika and polio?

Zika virus can trigger of Guillain-Barré syndrome (GBS), a rare condition in which a person’s immune system attacks the peripheral nerves and which may, in severe cases, can result in near-total paralysis. Acute flaccid paralysis (AFP) is an indicator of both GBS and polio.

As Guillain-Barré syndrome has been associated with Zika virus infection, increases in the incidence of AFP – routinely reported to the Global Polio Eradication Initiative – might provide a useful early warning for Zika virus outbreaks in resource-constrained settings. Researchers analysed data from the Pacific Islands to test this hypothesis.

How could the polio surveillance system help detect Zika virus outbreaks?

The researchers’ study, recently published in the WHO Bulletin, found that a significant increase in reported cases of AFP are correlated with Zika virus emergence on one island, Solomon Islands. The researchers had analysed published and unpublished data on Zika virus outbreaks that occurred between 2007 and 2015 in 21 Pacific Islands. They also analysed data from the Global Polio Eradication Initiative database on the reported and expected annual number of AFP in children younger than 15 years of age. However, the evidence was not conclusive to conclude that routinely reported AFP incidence data in children were useful for detecting emergence of Zika virus in in resource-constrained settings.

Could the polio surveillance system help estimate Guillain-Barré syndrome trends?

The analysis of the data above found no conclusive evidence that routinely reported cases of AFP in children were useful for detecting a significant increase in the number of people with Guillain-Barré syndrome (GBS) in countries and areas with small populations. While people of all ages can have GBS, the condition is more common in adults. In contrast, polio mainly affects children under 5 years of age, and hence the polio surveillance system looks for children under 15 years of age. The researchers concluded that data that include adult age groups may provide better evidence to determine whether AFP surveillance offers a suitable strategy for early warning for Zika virus outbreaks in low-resource countries.

Why was the study undertaken?

Monitoring the health situation and assessing trends is one of WHO’s core roles. We do this, among others, by gathering evidence on convenient, timely and cost-effective surveillance systems for our Member States. Hence,

  • in September 2016, the Emergency Committee under the International Health Regulations (IHR, 2005) regarding Zika and related complications had tasked WHO to provide appropriate guidance on effective surveillance of Zika virus disease in countries with high vulnerability and low capacity;
  • WHO’s interim guidance for the surveillance of Zika virus infection and Guillain-Barré syndrome recommends to review data from polio surveillance to estimate GBS trends.

What is the role of the polio surveillance network?

As part of the global polio eradication effort, an extensive and active network for the detection of acute flaccid paralysis has been established. It investigates more than 100 000 AFP cases every single year, all over the world. In fact, nine out of 10 Member States have strong AFP surveillance systems in place to detect, report and respond to cases of polio.

Is the polio surveillance network used for other diseases?

The network has been used effectively around the world to detect diseases other than polio such as measles, Ebola and yellow fever. For example, in Nigeria it was used effectively to stop Ebola. In India, the system is used to track and stop measles outbreaks.