Progress Toward Poliomyelitis Eradication --- India, January 2009--October 2010

Progress Toward Poliomyelitis Eradication --- India, January 2009--October 2010
Weekly
December 10, 2010 / 59(48);1581-1585

India is one of only four countries (including Afghanistan, Nigeria, and Pakistan) where wild poliovirus (WPV) transmission has never been interrupted (1). Historically, WPV transmission in India has centered largely in Uttar Pradesh and Bihar, two states with low routine vaccination coverage, large migrant and remote populations, and lower relative vaccine effectiveness than other areas of the country (2--4). However, during a 9-month period from November 2009 to August 2010, no WPV type 1 (WPV1) cases were reported in Uttar Pradesh or Bihar. This report summarizes the substantial progress made in India toward polio eradication during January 2009--October 2010, according to data reported as of December 4, and updates previous reports (2,4). During January--October 2010, only 40 WPV cases were confirmed in India, a 94% decrease from the 626 WPV cases confirmed during the same period in 2009; the decrease likely resulted, in large part, from the introduction of bivalent oral poliovirus vaccine types 1 and 3 (bOPV). Increasingly important contributors to WPV transmission are large migrant subpopulations; surveys have indicated that up to 11% of children aged <5 years in these subpopulations were missed during supplementary immunization activities (SIAs). Interruption of all WPV transmission in India will require maintaining high levels of immunity in Uttar Pradesh and Bihar and additional efforts directed toward children in migrant subpopulations that are not vaccinated as readily during SIAs.

Immunization Activities

Using population-based survey data, India estimated nationwide routine coverage with 3 doses of oral poliovirus vaccine (OPV) at 66% among children aged 12--23 months during 2007--2008, the most recent years for which coverage data were available (5). Routine coverage estimates in Bihar (53%) and Uttar Pradesh (40%) were among the lowest in the country (5).

SIAs* conducted in India during 2009--2010 (Figures 1 and 2) included two national immunization days (NIDs) each year. In addition, seven subnational immunization days (SNIDs) and four large-scale (multidistrict) mop-up† activities were conducted during 2009, and five SNIDs and three large-scale mop-ups were conducted during January--October 2010 (Figure 1). After introduction of bOPV in January 2010, six SIAs were conducted using bOPV.

In 2010, SIA monitoring data§ indicated >99% coverage among children aged <2 years in Bihar and >97% in Uttar Pradesh. After enhanced efforts during 2009--2010 to identify specific areas in other states where migrant populations resided, directed surveys conducted with specific migrant subpopulations (e.g., construction laborers, nomads, and brick kiln workers) after SIA rounds indicated that 3%--11% of children aged <5 years had been missed. In Uttar Pradesh during 2010, surveys after SIAs indicated that, on average, 4.1% of children in the migrant subpopulations, compared with 2.2% missed among children aged <5 years in the general population.

WPV Surveillance

Acute flaccid paralysis (AFP) surveillance. The national nonpolio AFP rate,¶ a measure of surveillance system sensitivity, was 11.4 per 100,000 children aged <15 years in 2009 and 11.1 per 100,000 (annualized) during January--October 2010. The highest state-level nonpolio AFP rates were in Bihar (33.9) and Uttar Pradesh (22.8) in 2010. Adequate stool specimen collection** in India was 83% in 2009 and 84% during January--October 2010.

Environmental surveillance. Wastewater testing for poliovirus began in Mumbai in January 2001 and in Delhi in May 2010. Although WPV was isolated frequently from samples taken in Mumbai in previous years, no WPV was detected in Mumbai wastewater in 2010. Environmental testing during May--August 2010 detected both WPV1 and WPV type 3 (WPV3) in wastewater at Delhi sites. Genetic analysis has suggested WPV circulation within Delhi was linked to 2009 WPV1 and WPV3 Bihar isolates. No WPV has been detected in environmental samples since mid-August.

Laboratory network. During January--October 2010, >90% of stool specimens submitted for virus isolation had laboratory results reported within 14 days of specimen receipt. The mean interval from onset of paralysis and confirmation of WPV isolation was 24 days.††

WPV Epidemiology

During all of 2009, a total of 741 WPV cases were reported in India from 56 districts in nine states of 35 states/union territories in India (Figure 3). During January--October 2010, a total of 40 WPV cases had been reported from 17 districts in seven states, a 94% decrease from the 626 WPV cases from 52 districts in nine states during the same reporting period in 2009. Among the 40 WPV cases reported in 2010, 28 (70%) occurred in children aged <2 years. Six (15%) of the 40 children had received 1--3 OPV doses, eight (20%) had received 4--7 doses, and 25 (63%) had received >7 doses; one child had unknown vaccination status. In Uttar Pradesh and Bihar, 19 cases had been reported from 10 districts; all of these patients had received >7 OPV doses. According to data reported as of December 4, 2010, during January--October 2010, a total of 17 WPV1 and 23 WPV3 cases were confirmed, representing a 78% decrease from 76 WPV1 cases and a 96% decrease from 550 WPV3 cases confirmed during the same period in 2009.

WPV1. In 2009, a total of 80 WPV1 cases were reported (including one case with both WPV1 and WPV3 isolated) from 35 districts in six states. During January--October 2010, a total of 17 WPV1 cases were reported from seven districts in five states. WPV1 isolates related to 2009 Bihar WPV1 strains have been isolated from AFP patients with onset of paralysis during January--October 2010 in West Bengal (five patients), Jharkhand (three), and Maharashtra (five). In addition, WPV1 strains circulating in Bihar during 2009 were associated with a WPV1 case in Jammu and Kashmir in 2010 after importation into Punjab in 2009. The most recent WPV1 case in India had onset on September 21 in West Bengal.

The last confirmed WPV1 case in Uttar Pradesh was in a patient with onset of paralysis on November 13, 2009. In Bihar, no WPV1 cases were reported from October 30, 2009, to August 7, 2010. Subsequently, three cases have been reported in a single Bihar district bordering Nepal (Champaran East), with onset in the most recent case on September 1. The recent Bihar outbreak began after an outbreak was identified in Nepal in May 2010 immediately across the border from Champaran East; WPV1 isolates from both areas are related to WPV1 strains circulating in Bihar during 2009.

WPV3. In 2009, a total of 661 WPV3 cases were reported from 47 districts in eight states; 569 (86%) were from Uttar Pradesh, and 79 (12%) were from Bihar. During January--October 2010, a total of 23 cases were reported from 12 districts in five states, compared with 550 cases from 43 districts in seven states during the same 10-month period in 2009. Of the 23 cases reported during January--October 2010, 10 (43%) were from Uttar Pradesh, six (26%) from Bihar, four (17%) from Jharkhand, two (9%) from West Bengal, and one (4%) from Haryana. The most recent WPV3 case in India had onset on August 31 in Jharkhand.

Reported by

Ministry of Health and Family Welfare, Government of India. National Polio Surveillance Project, World Health Organization, India; Regional Poliovirus Laboratory Network, Immunization and Vaccine Development Dept, World Health Organization Regional Office for South-East Asia. Div of Viral Diseases and Global Immunization Div, National Center for Immunization and Respiratory Diseases; CV Cardemil, MD, EIS Officer, CDC

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Progress Toward Poliomyelitis Eradication --- India, January 2009--October 2010