The World Health Organisation (WHO) has received notification of the detection of a circulating vaccine-derived type 2 poliovirus in Cameroon. The global health agency said the virus originated from Nigeria.
The alert was raised by the Global Polio Laboratory Network (GPLN).
According to a press statement by the UN health agency, the type 2 poliovirus was detected from an environmental sample collected on April 20 in a hospital in Northern Cameroon. The community where the hospital is located borders Borno State in Nigeria as well as Chad.
In this region, the vaccine coverage in 2018 for inactivated poliovirus vaccine (IPV1) and oral poliovirus vaccine (OPV3) was 73 per cent and 72 per cent respectively.
WHO said the virus was detected in an environmental sample only and no associated cases of paralysis have been detected so far.
It said genetic sequencing confirms that the isolate is associated with the ongoing cVDPV2 outbreak in neighbouring Nigeria which originated in Jigawa State and spread to other areas of Nigeria, as well as internationally to the Republic of Niger in 2018.
Nigeria Polio Status
Nigeria is one of the three countries – including Pakistan and Afghanistan – which are yet to eradicate wild poliovirus from their territories.
Nigeria had recorded significant progress and was on the verge of being declared polio-free until a case of polio was discovered in Borno in 2016.
This brought about a setback in getting a polio-free certification. With this, the government embarked on a rigourous polio vaccination campaign especially in the North-east, part of which Boko Haram insurgency had made inaccessible to health workers.
It was expected that if no new case of poliovirus is detected in Nigeria by August, Africa will attain the wild polio eradication goal.
Despite the rigorous vaccination campaign, Nigeria is still facing a new challenge of type 2 polio.
This year, new cases of type 2 polio have been reported in some states in the country. This is often caused by incomplete dosage of polio vaccination.
This is said to be spreading due to the migration of children from one region to another.
Public health response
In response to the situation, WHO said the Ministry of Health and local health authorities are providing monovalent type 2 oral polio vaccine (mOPV2) to tackle the problem.
“In the response to the cVDPV2 outbreak in Nigeria and across the Lake Chad sub-region (Chad, Cameroon, Niger and Nigeria) the Ministry of Health and local health authorities are providing monovalent type 2 oral polio vaccine (mOPV2) to curb the spread.
Also, “a thorough investigation of the incident is ongoing with the support of partners in the Global Polio Eradication Initiative (GPEI) and includes assessing the extent of circulation of this strain, identifying sub-national immunity gaps and supporting efforts to strengthen sub-national surveillance sensitivity,” it said.
WHO risk assessment
WHO in its assessment said the event highlights the risk of renewed international spread of cVDPV2 from Nigeria and the rest of the Lake Chad region, given the large-scale population movement; subnational immunity and surveillance gaps across the area.
“The detection of this cVDPV2 strain underscores the importance of maintaining high levels of routine polio vaccination coverage at all levels to minimize the risk and consequences of any poliovirus circulation,” the global health agency said.
WHO said it will continue to support the ongoing investigation and risk assessment by national authorities.
The UN health agency also advised all countries, particularly those reporting frequent travel to polio-affected countries and areas, to strengthen surveillance of acute flaccid paralysis (AFP) in order to rapidly detect imported cases and facilitate a rapid response.
All countries should maintain a high routine immunisation coverage at the district level to minimize the impact of new virus introduction.
WHO’s International Travel and Health recommends that all travellers to polio-affected areas be fully vaccinated against polio. Residents (and visitors for more than 4 weeks) from infected areas should receive an additional dose of OPV or IPV within 4 weeks to 12 months of travel.