jueves, 11 de agosto de 2011

Progress Toward Poliomyelitis Eradication --- Nigeria, January 2010--June 2011

full-text ► [large]Progress Toward Poliomyelitis Eradication --- Nigeria, January 2010--June 2011: "Progress Toward Poliomyelitis Eradication --- Nigeria, January 2010--June 2011
August 12, 2011 / 60(31);1053-1057

The Global Polio Eradication Initiative (GPEI) was launched by the World Health Assembly in 1988. By 2006, transmission of indigenous wild poliovirus (WPV) was interrupted in all countries except Nigeria, Afghanistan, Pakistan, and India (1). Among the 36 states and Federal Capital Territory of Nigeria, WPV transmission has persisted in eight northern states considered at high risk; in addition, four other northern states have been considered at high risk for WPV transmission (2). In these 12 high-risk states, type 2 circulating vaccine-derived poliovirus (cVDPV2) transmission also was observed during 2005--2011 (3,4). This report updates GPEI progress in Nigeria during January 2010--June 2011 (1,2) and describes activities required to interrupt transmission. In Nigeria, confirmed WPV cases decreased 95%, from 388 in 2009 to 21 in 2010; cVDPV2 cases decreased 82%, from 154 in 2009 to 27 in 2010. However, as of July 26, 2011, Nigeria had reported 24 WPV cases (including one WPV/cVDPV2 coinfection) and 11 cVDPV2 cases during January--June 2011, compared with six WPV cases and 10 cVDPV2 cases during January--June 2010. Despite substantial progress, immunization activities and surveillance sensitivity will need to be enhanced further to interrupt WPV transmission in Nigeria by the end of 2011.

Immunization Activities

The Nigeria routine immunization schedule recommends doses of trivalent OPV types 1, 2, and 3 (tOPV) at birth and, together with diphtheria-tetanus-pertussis vaccine (DTP), at ages 6, 10, and 14 weeks. Because reported OPV coverage can include doses administered during supplementary immunization activities (SIAs), coverage with DTP is a more accurate indicator of OPV administered through routine immunization. Nationally, the proportion of children aged 1 year who had received 3 doses of DTP (DTP3) was 40% in 2006 and 69% in 2010 as estimated by the World Health Organization (WHO) and the United Nations Children's Fund (UNICEF)* using administrative data and multiple surveys. DTP3 coverage in National Immunization Coverage Surveys (NICS) in the eight states† with persistent WPV transmission in 2006 and 2010 was 30% (range: 9%--52%) and 47% (range: 26%--89%), respectively, compared with national coverage of 54% in 2006 and 68% in 2010.

Bivalent OPV types 1 and 3 (bOPV) became available in 2010 and has largely replaced monovalent OPV type 1 (mOPV1) and type 3 (mOPV3) use in SIAs during 2010--2011. Three national SIAs were conducted in 2010 and two during January--June 2011. In the northern states, five subnational SIAs were conducted in 2010 and three during January--June 2011. Various combinations of mOPV1, mOPV3, bOPV, or tOPV were used during these SIAs (Figure 1).

The effectiveness of SIA implementation in the 12 high-risk states§ is monitored by surveys to look for children missed by SIAs in high-risk wards (i.e., subdistricts). The proportion of wards with >10% children missed by SIAs during January 2011--June 2011 was consistently >15% in six states (Kaduna, Kano, Katsina, Kebbi, Niger, and Yobe). The majority of children missed by SIAs lived in households not visited by SIA teams or were not present during vaccination team visits.

Vaccination recall histories of children with nonpolio acute flaccid paralysis (NPAFP) are used to estimate OPV coverage from routine immunization and SIAs among children aged 6--35 months. The proportion of children with NPAFP reported to have never received an OPV dose (i.e., zero-dose children) declined from 30.9% in early 2006 to 10.8% in early 2009 in the eight states with persistent transmission (5). During 2010--2011, downward trends continued (Table), but the overall proportion has not fallen below 5% and ranges as high as 16.7% in Borno. The proportion of children aged 6--35 months with NPAFP who have received ≥3 doses of OPV increased from 24% in early 2006 to 82% in early 2011(5). The targets for the 12 high-risk states are <10% zero-dose children and >80% children with NPAFP with ≥3 OPV doses. In 2011, nine states (Bauchi, Gombe, Jigawa, Kaduna, Katsina, Kebbi, Niger, Sokoto, and Zamfara) met both targets; Kano and Yobe met only the <10% zero-dose target; Borno met neither target.¶

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