Programmatic benefits of bivalent OPV - 'from bench to bush!'

Following the development and wide utilisation of monovalent oral polio vaccines (OPV) since 2005, transmission of indigenous wild poliovirus type 1 (WPV1) and wild poliovirus type 3 (WPV3) has been restricted to geographically limited areas of four endemic countries: Nigeria, India, Pakistan, and Afghanistan.

However, given the ongoing co-circulation of WPV1 and WPV3 in these areas, in November 2007, the Advisory Committee on Poliomyelitis Eradication (ACPE) recommended that the Global Polio Eradication Initiative (GPEI) exploit an opportunity to obtain clinical data on a bivalent OPV (containing type 1 and 3 serotypes) in a clinical trial.

In 2008-2009, the clinical trial was conducted in India (in Indore, Pune and Chennai), to compare the rate of seroconversion to each serotype in the bivalent OPV with that of the respective monovalent OPV and trivalent OPV. For both types 1 and 3 polio, bivalent OPV was found to be at least 35% more effective than trivalent OPV and almost as good as the monovalent OPVs. The ACPE reviewed the final trial results in November 2009 and concluded that the strategic use of bivalent OPV in supplementary immunization activities (SIAs) could be an important additional tool in polio eradication, in those areas where both serotypes are circulating.

Since then, bivalent OPV products from four vaccine manufacturers have been pre-qualified by WHO, while a further two applications for pre-qualification are pending. Between December 2009 and May 2010, over 300 million doses have been procured and utilized in nine countries, with a further rapid scale up of utilization expected throughout 2010 (Table 1). This new vaccine complements the existing arsenal of monovalent and trivalent OPVs, but fills a previously key gap by simultaneously generating immunity to both remaining WPV serotypes. The new bivalent OPV has greatly simplified the logistics of conducting SIAs, and it is anticipated that this tool could greatly accelerate eradication in some settings. The rapid scale-up of the new bivalent OPV is expected to be a cornerstone approach to optimizing SIA strategy during the life of the new GPEI Strategic Plan 2010-2012.

The field evaluation, development and availability of bivalent OPV further reflects the dynamic nature of the GPEI: evidence-based programming, ongoing learning and tactical adjustments to provide the best possible response to field challenges and requirements (Figure 1). The very rapid process from field test to actual field application of this vaccine was the result of an extraordinary collaboration between WHO, UNICEF, vaccine manufacturers and national regulatory agencies.

Table 1 - Utilization of bivalent OPV, by country, during SIAs

Country	Date of SIA	Number of doses of bivalent OPV used (in millions)
Afghanistan	15 December 2009	4.6
	24 January 2010	0.5
	14 February 2010	4.6
	14 March 2010	9.4
Pakistan	15 February 2010	38.5
	15 March 2010	19.2
	24 May 2010	19.2
Sudan	22 February 2010	8
	29 March 2010	3.4
India	10 January 2010	15.6
	7 February 2010	40.6
	25 April 2010	44.5
	23 May 2010	39.4
Nepal	10 April 2010	5.8
	15 May 2010	5.8
Benin	24 April 2010	3.3
Niger	26 March 2010	5.1
	24 April 2010	5.1
Nigeria	30 January 2010	51.8
	24 April 2010	18.6
GRAND TOTAL		344.4