The number of wild poliovirus type 1 (WPV1) cases have topped 300 globally as the bad situation in Pakistan continues. With reports of 14 additional cases from Pakistan and one from Afghanistan, the global total has reached 306.
One new wild poliovirus type 1 (WPV1) case was reported in the past week in Afghanistan in Kandahar district, with onset of paralysis on the 5 November. The total number of WPV1 cases for 2014 in Afghanistan is now 21, according to the Global Polio Eradication Initiative (GPEI).
In Pakistan, fourteen new wild poliovirus type 1 (WPV1) cases were reported in the past week. The total number of WPV1 cases in Pakistan in 2014 is now 260, compared to 64 at this time last year.
To make things worse, on Wednesday four more health workers who were administering polio vaccines were killed by yet unknown gunmen. This brings the total of anti-polio workers killed to 65 in the past two years.
Despite the trouble in Pakistan, reports out of Africa offer something to cheer about. The third polio endemic country, Nigeria, has not reported a WPV-1 case since July. Nigeria’s total WPV-1 case count is only six, this compares with 53 cases in 2013.
In addition, the GPEI notes that for the first time ever, only 1 case of wild poliovirus has been reported in Africa in the last 4 months, despite the high season for polio transmission. The most recent case had onset of paralysis on 11 August in Somalia.
Plans to switch to a bivalent oral polio vaccine by early 2016 is on track. At the end of October, the SAGE (an independent expert body that advises WHO) met to assess progress toward polio eradication. The group concluded that preparations are on track to switch from trivalent to bivalent OPV in routine immunisation programmes.
This is an important step in eradication efforts as, on very rare occasions, the weakened forms of the virus in OPV can lead to cases of circulating vaccine-derived poliovirus (cVDPV), particularly in communities where children have a very low level of immunity.
Trivalent OPV contains weakened forms of all three strains of the poliovirus. Since circulation of WPV2 hasn’t been detected since 1999, preparations are now underway to begin using only bivalent versions of OPV that protect against WPV1 and WPV3. This transition is crucial, as bivalent OPV does not contain the type 2 component which accounts for 90% of cVDPV cases worldwide. Recent cases of vaccine-derived poliovirus in South Sudan and Madagascar, and ongoing outbreaks in Nigeria and Pakistan, highlight the importance of removing OPV (beginning with the type 2 OPV) in addressing the very small but real risk of vaccine-derived poliovirus.
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