Progress towards interruption of wild poliovirus transmission in 2005/Interruption de la transmission du poliovirus sauvage, 2005: progres accomplis.

Following the 1988 World Health Assembly resolution (1) to eradicate poliomyelitis globally, the number of countries endemic for polio declined from 125 in 1988 to only 4. After more than a year without transmission of indigenous wild poliovirus, Egypt and Niger were removed from the list of polioendemic countries (2) in January 2006, demonstrating continued progress towards the goal of global eradication.

In 2005, the endemic Asian countries (particularly India and Pakistan) moved closer to the eradication goal. Of the 22 previously polio-free countries (3) that were reinfected between 2003 and 2005, only 8 (in Africa and Asia) reported wild poliovirus transmission since mid-2005, and polio was again on the verge of interruption in 7 of 8 countries (all but Somalia) by early 2006. (4)

Important innovations in 2005 included the re-licensing and use of monovalent type 1 (mOPV1) and type 3 (mOPV3) oral poliovirus vaccines and, particularly in endemic countries, the increase in the number and quality of supplementary immunization activities (SIAs), the systematic engagement of local leaders during SIAs and a new focus on SIA "transit strategies" to target children who move through major train and bus transit sites.

By the end of 2005, 6 states in northern Nigeria, where SIAs continue to miss >40% of target children, emerged as being the greatest risk for renewed international spread of wild polioviruses. This report describes developments in the implementation of each of the 4 polio eradication strategies from January 2005 to March 2006 and outlines the remaining challenges as well as the need for decisive action to interrupt transmission globally.

Routine oral poliovirus vaccination. Global routine vaccination coverage among infants with 3 doses of OPV (OPV3) was estimated at 80% in 2004, (5) the most recent year with fully reported data. OPV3 coverage in 2004 varied among WHO regions, from 69% in the African Region (up from 65% in 2003) to 94% in the European Region, with considerable variation between country-level estimates within each region. OPV3 coverage in currently polio-endemic countries in 2004 was estimated at 39% in Nigeria, 66% in Afghanistan, 65% in Pakistan and 70% in India. In each country, national estimates may hide considerable regional variations and "immunity gaps" at the subnational level.

Important improvements in routine coverage were observed in several large African countries (including Democratic Republic of the Congo and Ethiopia). These improvements were driven primarily by the increased use of the RED (reach every district) approach, which relies on key polio eradication strategy elements, including microplanning, improved supervision and community involvement, to establish outreach services.

Supplementary immunization activities. In 2005, a total of 234 SIAs using OPV (153 national immunization days (NIDs), 69 sub-NIDs (SNIDs) and 12 mop-up campaigns) were conducted in 51 countries, administering 2.2 billion doses of OPV to 371 million children aged <5 years. Given the substantial type-specific gains in immunity conferred by monovalent OPVs compared with trivalent OPV, mOPV1 was rapidly re-licensed and administered during SIAs in 12 countries. Of the 2.2 billion OPV doses used in SIAs, 473 million doses (21.5%) were mOPV1 and 8.4 million doses (3.8%) were mOPV3.

Of the 234 SIAs conducted in 2005, 59 were in the 6 endemic countries in 2005: 17 in India (2 NIDs and 15 SNIDs), 11 in Pakistan (8 NIDs and 3 SNIDs), 12 in Afghanistan (4 NIDs, 6 SNIDs and 2 mop-up campaigns), 7 in Egypt (6 NIDs and 1 SNID), 5 NIDs in Niger and 7 NIDS in Nigeria (4 NIDs and 3 SNIDs).

Of the 51 countries conducting SIAs in 2005, 23 participated in synchronized SIAs across west and central Africa, including the Sudan.

In 2005, 20 of the 22 previously polio-free countries reinfected since 2003 conducted a total of 114 SIAs (87 NIDs, 19 SNIDs and 8 mop-ups). Also in 2005, 25 polio-free countries (18 in the African Region, 3 in the Eastern Mediterranean Region and 4 in the Western Pacific Region) conducted a total 61 SIAs, including 37 NIDs, to increase population immunity as a precaution to prevent the spread of possible virus importations.

Acute flaccid paralysis surveillance and polio laboratory network. The quality of surveillance for acute flaccid paralysis (AFP) is monitored by 3 main performance indicators: (i) the rate of AFP cases not caused by wild poliovirus (the "non-polio AFP rate," target for certification: [greater than or equal to] 1 case per 100 000 population aged <15 years); (ii) the proportion of AFP cases from whom adequate stool specimens were collected (target for certification: [greater than or equal to] 80%); (iii) the proportion of stool specimens processed in a laboratory accredited by WHO (target: 100%).

In 2005, all WHO regions maintained the overall sensitivity of AFP surveillance to detect paralytic polio cases at certification-standard levels (Table 1). AFP reporting continued to improve in the 3 regions with endemic poliovirus transmission regions (African, Eastern Mediterranean and South-East Asia). There was an overall increase in AFP reporting globally of 43%, from 42 511 cases in 2004 to 61 606 cases in 2005, largely because of increased reporting from India (80% of the overall increase), Nigeria and Pakistan. All endemic and reinfected countries with reported cases in 2005 reached non-polio AFP rates of at least 2/100 000 (range: 2.1-6.5).

Although the certification target for AFP reporting (i.e. non-polio AFP rate of at least 1/100 000) remains unchanged, in 2005 the global Advisory Committee on Polio Eradication (ACPE) endorsed a new minimum operational target non-polio AFP rate of at least 2/100 000 for all endemic countries and countries at high risk of wild virus importation, (6) to accelerate the detection of and response to circulating polioviruses.

In 2005, WHO fully accredited 97% of the 145 laboratories in the global poliovirus laboratory network, which analysed more than 120 000 stool samples that year. Parallel testing arrangements ensured that even specimens from …