Progress Toward Poliomyelitis Eradication --- India, January 2006--September 2007

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India is one of four countries where wild poliovirus (WPV) transmission has never been interrupted (the others are Afghanistan, Nigeria, and Pakistan) (1). An outbreak of poliomyelitis cases caused by WPV type 1 (WPV1) occurred in India in 2006, primarily in the northern states of Uttar Pradesh and Bihar, where polio remains endemic. This outbreak resulted in the greatest annual number of cases of poliomyelitis in India since 2002. In response, the Government of India and its partners implemented additional vaccination measures based on recommendations from the India Expert Advisory Group on Polio Eradication. These measures focused predominantly on use of monovalent oral poliovirus vaccine type 1 (mOPV1),* which has higher efficacy against WPV1 than trivalent OPV (tOPV) (2,3). As a result, WPV1 cases in India decreased approximately 84% to 66 cases during January--September 2007, compared with 405 cases during the corresponding period in 2006. In western Uttar Pradesh, a state in which multiple risk factors have made interruption of WPV transmission challenging, five WPV1 cases have been reported this year, compared with 299 during the same period in 2006. However, a WPV type 3 (WPV3) outbreak also has been reported, with 261 cases occurring through September 30, 2007, primarily in the northern states where polio remains endemic. This report summarizes progress toward polio eradication in India during January 2006--September 2007 and highlights the challenges and strategic adaptations of eradication measures (4).

Acute Flaccid Paralysis (AFP) Surveillance

AFP surveillance^† is fundamental to monitoring progress toward polio eradication; surveillance quality is monitored according to World Health Organization (WHO) operational targets.^§ The national nonpolio AFP rate (i.e., the number of nonpolio AFP cases per 100,000 population aged <15 years) was similar during January--December 2006 (7.35 cases) and January--September 2007 (7.83 cases). In 2006 and 2007, nonpolio AFP rates were highest in Uttar Pradesh (15.80 cases and 15.32 cases, respectively) and Bihar (19.00 cases and 20.97 cases, respectively). Adequate stool-specimen collection nationally was 82% in 2006 and 85% during January--September 2007.

Virologic testing of stool specimens from AFP patients in India is conducted at eight laboratories, all of which are accredited by WHO as part of the Global Polio Laboratory Network (5). These laboratories have had an increased workload, with 62,642 specimens processed in 2006 and 58,966 specimens processed during January--September 2007, compared with 52,516 in 2005. Despite this workload, laboratories reported a primary virus isolation result within 28 days of receipt of specimen for 99% of specimens in 2006. The mean interval from receipt of primary isolation results to final intratypic differentiation of poliovirus (i.e., wild or vaccine related) was 8.3 days in 2006.

WPV Incidence

In 2006, India reported a total of 676 polio cases from 114 districts. In 2007, India had reported 326 polio cases from 68 districts, with onset of paralysis during January 1--September 28, compared with 416 cases from 73 districts for the same period in 2006 (Figures 1 and 2). The majority of cases occurred in children aged <2 years in both 2006 (69%) and 2007 (63%).

WPV1. In 2006, a total of 648 (96%) reported polio cases were WPV1; of these, 581 (85%) occurred in Uttar Pradesh (520 cases) and Bihar (61 cases). The tenfold increase in WPV1 circulation in 2006 compared with 2005 (648 cases versus 62 cases) was the result of an outbreak that originated in western Uttar Pradesh and spread to the rest of Uttar Pradesh and 15 other states.

As of October 20, 2007, a total of 66 WPV1 cases had been reported from 40 districts, compared with 405 cases from 73 districts during the same period in 2006. In Uttar Pradesh, 21 WPV1 cases had been reported in 2007, compared with 347 for the same period in 2006. Although the typical peak season for poliovirus transmission is June--September, only five of the 21 cases (24%) in 2007 occurred during this period. Within western Uttar Pradesh, only five cases of WPV1 have been reported in 2007, compared with 299 cases for the same period in 2006 and 19 cases for the same period in 2005. However, WPV1 continues to circulate in Bihar, where 33 (50%) of the 66 WPV1 cases have been reported this year, compared with 28 cases for the same period in 2006. Of 433 blocks^¶ within Bihar, 268 (62%) have not reported any WPV1 cases since 2001, 93 (21%) have reported only a single case, and 72 (16%) are blocksat high risk for recurrence of WPV1.

WPV3. In 2006, a total of 28 WPV3 cases were reported, all from districts of western Uttar Pradesh. However, in 2007, the number of WPV3 cases has increased to 261, with 231 (83%) occurring in western Uttar Pradesh. During the peak transmission season (June--September), WPV3 spread to areas outside of western Uttar Pradesh, with seven cases reported in the neighboring areas of Delhi, Uttarakhand, Haryana, and Rajasthan; three cases in central Uttar Pradesh; and 23 cases in Bihar. Before this importation, no cases of WPV3 had been reported in Bihar since January 2004.

Immunization Activities

Reported routine vaccination coverage of infants with 3 doses of OPV was 68% in India in 2006 (6). In Bihar and Uttar Pradesh, coverage was lower (48% and 44%, respectively). India continues to implement strategies to improve routine vaccination services in these areas (3).

In 2006, India conducted 10 supplementary immunization activities (SIAs),** which included two rounds of national immunization days (NIDs), targeting 172 million children, and eight rounds of subnational immunization days (SNIDs) in areas with detected WPV circulation or areas at high risk for WPV circulation. During January--September 2007, India conducted nine SIAs (two rounds of NIDs and seven of SNIDs) (Figure 3).

Since mOPV1 and monovalent oral poliovirus vaccine type 3 (mOPV3) became licensed in India in 2005, their use has become an integral part of SIAs in Uttar Pradesh, Bihar, and areas with transmission of imported virus. SNIDs have been conducted every 3--6 weeks in Uttar Pradesh and Bihar, primarily with mOPV1. One SNID round in 2006 (December) and two SNID rounds in 2007 (March and July) with mOPV3 were conducted in selected districts of western Uttar Pradesh and neighboring states with WPV3 circulation. Five SIA rounds with tOPV were conducted in central and eastern Uttar Pradesh during 2006, and one SNID round with tOPV was conducted in April 2007 in all of Uttar Pradesh. In Bihar, nine SIAs using mOPV1 have been conducted in 2007. SNIDs with mOPV3 were conducted in October 2007 after confirmation of WPV3 cases. In addition, in 2007, a new vaccination strategy targeting migrant populations was implemented in two SNIDs. A total of 1.4 million children were administered mOPV1 in the states of Gujarat, Haryana, and Punjab, which have numerous migrant laborers from Uttar Pradesh and Bihar.

SIA quality^†† has improved from 2006 to 2007. The percentage of missed houses in Moradabad^§§ in western Uttar Pradesh decreased approximately 50%, from 12% in January 2006 to 6% in April 2007; the percentage of missed houses remained at 6%--8% during all subsequent rounds. In Bihar, the percentage of missed houses remained at approximately 12%--14% (3).

Reported by: Ministry of Health and Family Welfare, Government of India; National Polio Surveillance Project; Immunization and Vaccine Development Dept, WHO Regional Office for South-East Asia; UNICEF, New Delhi; Poliovirus Laboratory Network, Ahmedabad, Bangalore, Chennai, Coonoor, Kasauli, Kolkata, Lucknow, and Mumbai, India. Vaccines and Biologicals Dept, WHO, Geneva, Switzerland. Div of Viral Diseases and Global Immunization Div, National Center for Immunization and Respiratory Diseases; AE Sever, MD, EIS Officer, CDC.

Editorial Note:

India has continued to make progress towards polio eradication despite a WPV1 outbreak in 2006 and an ongoing WPV3 outbreak in 2007. Based on recommendations of the Global Advisory Committee on Polio Eradication and the India Expert Advisory Group on Polio Eradication, India has prioritized elimination of WPV1 because this virus type has a greater likelihood of causing paralytic disease, has been responsible for >90% of polio cases in the country during the past 5 years, and has been the source for reinfection of six polio-free countries (Angola, Bangladesh, Democratic Republic of the Congo, Myanmar, Namibia, and Nepal). Consequently, the intensified use of mOPV1 during frequent, large-scale SIAs coupled with improvements in the quality and consistency of SIA coverage has been critical to substantially curtailing the outbreak of WPV1. For the first time, this strategy has led to record low numbers of WPV1 cases in the areas that previously had the highest incidence. The limited number of WPV1 cases in western Uttar Pradesh and the continued decline of WPV1 incidence throughout the peak transmission season suggest that an unprecedented opportunity exists to end WPV1 transmission in Uttar Pradesh.

Transmission of WPV1 in Bihar continues despite intensified measures. However, after the series of mOPV1 SIAs implemented during 2006 and 2007, WPV1 transmission is primarily localized in four north/central districts. Eradication activities in high-risk blocks of Bihar are hindered by several operational difficulties, including extensive flooding during the rainy season. Both Uttar Pradesh and Bihar remain areas at risk for ongoing transmission because of multiple factors, including high population density, a large birth cohort, poor sanitation, and high population mobility.

The current WPV3 outbreak is not unexpected. Routine vaccination rates in Uttar Pradesh and Bihar remain low, and the SIA strategy has focused on WPV1 elimination with preferential mOPV1 use for most rounds in areas of WPV transmission. Because of its higher level of transmissibility, WPV1 is more likely to result in wide geographic spread than WPV3. Most of the WPV3 cases in 2007 occurred in certain districts of western Uttar Pradesh that had never conducted an mOPV3 SIA until July 2007.

More frequent, higher quality SIAs have contributed to decreased transmission of WPV. Since early 2006, interventions such as involvement of volunteer public health workers in Uttar Pradesh and Bihar, categorization and tracking of houses with missed children, vaccination of children at congregation and transit sites, and improved identification and vaccination of migratory populations have been implemented. In addition, the governments of Uttar Pradesh and Bihar have begun tracking newborns to increase the number of children aged <2 years who are vaccinated.

The progress toward elimination of WPV1 in western Uttar Pradesh indicates that poliovirus transmission can be interrupted in India. Sustaining this progress in Uttar Pradesh, reducing the number of WPV1 cases in Bihar, and controlling the WPV3 outbreak are critical. Judicious, intermittent, and timely use of WPV type-specific mOPV, guided by epidemiology, are essential to stopping WPV1 and WPV3 transmission in India in the near future. Eradication of polio in India will require continued diligence and collaboration among the Government of India, governments of Uttar Pradesh and Bihar, and partner organizations.^¶¶

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