Progress towards interrupting wild poliovirus transmission, January 2006-May 2007/Interruption de la transmission du poliovirus sauvage: progres accomplis entre janvier 2006 et mai 2007.

Transmission of wild poliovirus (WPV) has never been interrupted in 4 countries (Afghanistan, India, Nigeria and Pakistan). (1,2,3,4) During 2006 and the first half of 2007, progress continued towards the goal of global polio eradication. Continuing challenges to be met include intense WPV circulation of WPV in northern India, low coverage during supplementary immunization activities (SIAs) for oral polio vaccine (OPV) in Nigeria, and security problems that prevent health workers gaining access to children during SIAs in the border area between Afghanistan and Pakistan. Programmatic strategies designed to address these challenges included implementation of the widespread use of type 1 monovalent OPV (mOPV1), implementation of targeted strategies to reach more children through SIAs, including cross-border synchronization of polio campaigns, and the introduction of new laboratory procedures to confirm cases more rapidly. This report summarizes these strategies and the overall progress made towards attaining the goal of eradicating polio globally.

Routine OPV vaccination

Routine immunization remains an integral component of the Polio Eradication Initiative. Global coverage of routine vaccination for infants with 3 doses of OPV (OPV3) was estimated at 78% in 2005, (5) the most recent year with fully reported data. In 2005, estimated routine coverage of OPV3 varied among WHO regions, from 63% in the South-East Asia Region and 69% in the African Region to 84% in the Eastern Mediterranean Region and 87% in the Western Pacific Region. Coverage of OPV3 in the European Region and the Region of the Americas was >90%. In the 4 remaining polio-endemic countries, OPV3 coverage was estimated at 39% in Nigeria, 58% in India, 76% in Afghanistan and 77% in Pakistan. In each country, national estimates mask considerable subnational variations, and areas of lower coverage have been reported in regions where there is ongoing polio transmission (for example, northern Nigeria and the northern Indian states of Bihar and Uttar Pradesh).

Supplementary OPV immunization activities in 2006

In 2006, 187 SIAs with OPV were conducted in 36 countries (86 national immunization days, 84 subnational immunization days and 17 mop-up rounds), using a total of 2.12 billion doses of OPV and delivering them to 375 million children aged <5 years. The use of mOPV1 increased from 22% of all administered doses in 2005 to 46% in 2006, reflecting a programmatic shift in campaign strategy. Altogether, 58 (31%) of the 187 SIAs were conducted in the 4 polio-endemic countries: 17 each in India and Pakistan and 12 each in Afghanistan and Nigeria. Of the remaining SIAs in 2006, 78 (42%) were conducted in 12 reinfected countries reporting polio cases, and 51 (27%) were conducted in 20 countries without WPV-confirmed cases.

In 2006, new strategic approaches were employed in the 4 polio-endemic countries to improve the quality of SIAs. In mid-2006, Nigeria initiated a new strategy of offering other vaccines (measles and diphtheria-tetanus-pertussis) and health interventions (bednets, deworming medication) in addition to OPV during polio SIAs; these days were referred to as "immunization-plus days". (2) Polio-endemic countries use the OPV immunization status of non-polio acute flaccid paralysis (AFP) cases as a proxy to assess the level of immunity against polio in the population. The proportion of non-polio AFP cases who had never received any dose of OPV before ("zero-dose" children) in the northern states of Nigeria dropped from >50% at the end of 2005 to an average of 20% by the end of 2006. In India, in response to an outbreak in 2006, the government increased the number of large-scale SIAs occurring in the highest-risk districts of Bihar and western Uttar Pradesh (using mainly mOPV1) and concentrated on improving the coverage of children aged <2 years. In Afghanistan, a new multipronged approach included cross-border synchronization of polio campaigns with Pakistan.

Acute flaccid paralysis surveillance

The quality of AFP surveillance is monitored by 3 main performance indicators:

(1) the rate of AFP cases not caused by WPV (the "nonpolio AFP rate"). The target for quality of AFP surveillance sufficient to allow certification as polio-free is >1 case per 100 000 people aged <15 years;

(2) the proportion of AFP cases with adequate stool specimens. Adequate specimens are defined as 2 specimens collected [greater than or equal to] 24 hours apart within 14 days of the onset of paralysis. These must be shipped on ice or frozen ice packs to a WHO-accredited laboratory and must arrive at the laboratory in good condition. The target for certification is to collect adequate specimens from 80% or more of all AFP cases;

(3) the proportion of stool specimens processed in a WHO-accredited laboratory. The certification target is 100%.

In 2006, all WHO regions maintained the quality of AFP surveillance at levels of standard certification (Table 1). There was a 9.8% increase in AFP reporting globally, from 62 434 cases in 2005 to 68 576 cases in 2006, mainly as a result of increased reporting from India, Nigeria and Pakistan. In 2005, the global Advisory Committee on Polio Eradication endorsed a new minimum operational target of a non-polio AFP rate of 2/100 000 people aged <15 years for all endemic countries and for …