On August 21 this year, Nigeria crossed an important milestone in the eradication of polio when it successfully completed three successive years without a single case of wild poliovirus. The official announcement by the World Health Organisation is expected by early next year.

On August 21 this year, Nigeria crossed an important milestone in the eradication of polio when it successfully completed three successive years without a single case of wild poliovirus. A country is said to have eradicated polio when no fresh case of wild poliovirus is reported for three successive years. The last case of type 1 wild poliovirus was reported in August 2016 in Borno state, in the northeast. The official announcement by the World Health Organisation is expected by early next year.

With Nigeria almost winning the war against the wild polio virus, the polio endgame is getting closer. Today, wild poliovirus is endemic only in two countries — Pakistan and Afghanistan. Global eradication of wild poliovirus will depend primarily on stopping the disease in Pakistan and Afghanistan. As long as polio exists in any part of the world, children are at threat everywhere.

Just as it appeared to be easy to snuff out the virus in these two Asian countries, there has been a spike this year. As on August 28 this year, there have been 13 and 58 wild poliovirus cases reported in Afghanistan and Pakistan, respectively. Compared with 2018, the number of cases this year in Afghanistan has nearly halved while it has increased nearly four-fold in Pakistan.

After being removed from WHO’s list of polio endemic countries in September 2015, Nigeria came close to eliminating polio the very next year. After not recording a single case of polio for two successive years, Nigeria faced a setback in July-August 2016 when three fresh cases were reported. The wild virus strain in question that caused the fresh cases was found to be linked to the virus detected in 2011 in Borno, indicating that the virus strain was still present in the environment.

Though a setback, the fresh outbreak in 2016 was not unsurprising. After all, health-care workers have not been able to access as much as 60% of settlements in Borno due to decade-long insurgency in northeast Nigeria. As a result, about 500,000 children in Borno were deprived of health services by 2016.

Like in the case of northwest Pakistan in the case of polio a few years ago and the Democratic Republic of Congo in the latest outbreak of Ebola, Nigeria too had to rely on security personnel to escort health workers in Borno so children could be immunised. But unlike in other countries, Nigeria faced a unique problem. Certain areas were out of bound for health care workers and access was limited to only military personnel. Nigeria came up with a unique strategy to reach out to children in such areas by training the military personnel to double up as vaccinators.

These strategies have borne fruits. Health workers accompanied by security personnel have been able to immunise 80% of children with three doses of the vaccine containing only type 1 and type 3 polio viruses. Military personnel who themselves immunised the hard-to-reach children were able to reach 26%.

As per a July 2019 paper, the success of the two strategies notwithstanding, about 60,000 children are yet to be vaccinated in the insurgent-held areas; the true status of wild poliovirus in these children remains unknown.

Even as wild poliovirus appears to be tamed in Nigeria, as on August 28, 2019, the weakened type 2 virus used in oral polio vaccine had turned virulent and caused 16 cases of paralysis, down from 34 last year. Though vaccine-derived polio cases will not come in the way of Nigeria being certified as polio-free, multiple outbreaks of such kind are as concerning as the circulation of wild polio virus type 1 in Pakistan and Afghanistan. Of particular concern is the emergence of new strains of vaccine-derived virus in areas where oral vaccine containing only type 2 has been used, and the recent spread of vaccine-derived virus into southern Nigeria.