Poliomyelitis

Since 1988, the global incidence of polio has decreased by more than 99%, and three World Health Organization (WHO) regions (Americas, Western Pacific, and European) have been certified as polio-free (1). India, the largest of the six countries where polio remains endemic, experienced a large polio outbreak (1,600 cases) in 2002 (2). Since then, the Government of India (GOI) has accelerated its polio eradication activities by increasing the number and quality of supplementary immunization activities (SIAs), * which reduced the number of reported cases to 225 in 2003, 134 in 2004, and 18 in 2005 (as of June 18) (3). During 2004 and early 2005, taking advantage of the geographic restriction of wild poliovirus (WPV) circulation, GOI and its partners launched several immunization and surveillance strategies to maximize the probability of eliminating poliovirus transmission in India. With continued high-quality interventions, interruption of WPV transmission in India by the end of 2005 appears feasible. This report summarizes progress toward polio elimination during January 2004--May 2005 toward that end.

Acute Flaccid Paralysis (AFP) Surveillance

Since 2000, India has exceeded the WHO-established AFP surveillance quality targets (i.e., a nonpolio AFP rate of [greater than or equal to] 1 case per 100,000 population aged <15 years and adequate stool specimen collection ([dagger]) from [greater than or equal to] 80% of AFP cases). During 2004, the nonpolio AFP rate was [greater than or equal to] 1 case per 100,000 in 29 of India's 35 states (representing more than 99% of India's population). Adequate stool specimen collection for [greater than or equal to] 80% of AFP cases was reported from 26 states, with adequate specimen collection at 70%-80% in the remaining nine states.

AFP surveillance in India is facilitated through a network of WHO surveillance medical officers (SMOs) ([section]) who assist national, state, and local health authorities. Since May 2004, SMOs have accelerated efforts to detect and investigate all AFP cases, resulting in increased nonpolio AFP rates nationally, particularly in the states of Bihar and Uttar Pradesh, where polio remains endemic. During January-May 2005, compared with the same period in 2004, approximately twice as many AFP cases were detected and investigated in India. Adequate stool specimen collection remained above 80% in Uttar Pradesh and increased from 77% to 83% in Bihar (Table).

Virologic testing of stool specimens from AFP patients is conducted at eight national laboratories, all of which are accredited by WHO as part of the Global Poliovirus Laboratory Network. These laboratories perform primary isolation of polioviruses. Two of the laboratories (Chennai and Lucknow) also serve as upgraded national laboratories performing intratypic differentiation (ITD); one laboratory, the Enterovirus Research Centre (ERC) (Mumbai), functions as one of seven Global Specialized Poliovirus Laboratories and performs genetic sequencing of all poliovirus isolates in India. The laboratories have sustained high levels of performance despite an increased workload (33,272 specimens from AFP cases tested in 2004, compared with 16,403 specimens in 2003). For 97% of specimens, results of primary virus isolation in 2004 were communicated to the program within 28 days of specimen receipt in the laboratory. The mean interval from receipt of primary culture results to receipt of ITD results was 8 days (range: 2-21 days).

WPV Incidence

India reported 134 polio cases with patient onset of paralysis in 2004, compared with 225 reported cases in 2003. Of the 134 cases, 127 (95%) had isolation of WPV type 1 (P1) and seven cases (5%) had isolation of WPV type 3 (P3). As of June 18, 2005, India had reported 18 polio cases with onset in 2005: eight from Bihar (most recent case with onset on May 8, Araria district), seven from Uttar Pradesh (most recent case with onset on April 19, Ferozebad district), and one each front the states of Delhi, Jharkhand, and Uttaranchal (Figure 1). All 18 cases reported in 2005 were caused by P1; the most recent P3 case reported from India had onset in December 2004 in Rampur District, Uttar Pradesh.

All WPVs isolated in India are sequenced across the ~900-nucleotide interval encoding the major capsid protein (VP1) at ERC, and results are analyzed to determine the likely origin (by state and district) of the virus. The number of distinct genetic clusters ([paragraph]) of P1 decreased from 10 in 2003 to three in 2004 and two in 2005 (as of June 18). Only one P3 cluster was detected in 2004, with a single case in Bihar in January 2004; a distinct subcluster of lineages was detected in western Uttar Pradesh, including the most recent Indian P3 cases in December 2004.

Through weekly environmental sewage sampling in three urban wards of Mumbai, P1 was detected from late 2003 through most of 2004. During 2004, three P1 cases were reported from Mumbai and nearby districts, with onset on May 26 (Mumbai), July 10 (Thane district), and November 3 (Nasik district). As of June 18, no polio cases have been reported from Mumbai during 2005, but P1 was detected during April 2005 in environmental samples from two of the three sampled wards. Genetic sequencing of poliovirus isolates from sewage and cases in Mumbai and nearby districts indicate that all originated front Bihar or Uttar Pradesh.

Immunization Activities

Surveys indicate that routine vaccination coverage of infants with 3 doses of oral poliovirus vaccine (OPV), one of the four main polio eradication strategies, continues to be low in the remaining states where polio is endemic (Bihar: 21.1%; Uttar Pradesh: 41.4%). In April 2004, GOI, in partnership with WHO and UNICEF, initiated a strategic plan to strengthen routine childhood immunization in the polio-endemic districts of western Uttar Pradesh (Figure 2).

To sustain the impact of SIAs conducted in 2003, GOI conducted eight SIA rounds during 2004, including five nationwide rounds and three subnational rounds in states and districts in which WPV had been detected or that were at high risk for WPV circulation. During the first 5 months of 2005, four SIAs were conducted, including two national rounds and two subnational rounds in Mumbai and states with populations at high risk (Bihar, Delhi, Jharkhand, Uttaranchal, Uttar Pradesh, and West Bengal). During late 2004 and early 2005, additional personnel (from GOI, WHO, UNICEE Rotary International, and the Child Survival Collaborations and Resources [CORE] group of private voluntary organizations) were deployed to assist in planning and implementing intensified SIAs in Bihar, Mumbai, and Uttar Pradesh. Increased emphasis was placed on developing communication and other strategies to target underserved population groups missed during previous SIAs. Mobile teams vaccinated children at major transit points (e.g., railway and bus stations) and on moving trains, resulting in vaccination of an additional 5 million children. External monitoring of the April 2005 SIA round indicated high coverage of populations in areas of high risk, with an estimated 5.6%, 3.6%, and 2.8% of children remaining unvaccinated in western Uttar Pradesh, Bihar, and Mumbai, respectively.

In December 2004, the India Expert Advisory Group recommended acceleration of the development and licensing of monovalent OPV type 1 (mOP1) for use in SIAs (4). One dose of mOP1 elicits a stronger type 1-specific immune response, compared with 1 dose of trivalent OPV, for which the type 2 and 3 vaccine components interfere with the response to the type 1 component (5-7). In the absence of P2 (eliminated worldwide since 1999) and with P3 circulation in India localized and possibly eliminated, mOP1 is expected to optimize seroconversion among vaccine recipients.

Through close cooperation among GOI, vaccine manufacturers, and partner agencies, mOP1 was developed, licensed, and used during the SIA rounds of April, May, and June 2005 in Bihar, Uttar Pradesh, Mumbai, Delhi, and certain districts of Uttaranchal. Trivalent OPV continues to be used in the routine childhood immunization program and in SIAs in states that are not at high risk for WPV circulation.

Editorial Note: The polio eradication program in India continues to improve, particularly in the states of Bihar and Uttar Pradesh, where poliovirus is endemic. The number of WPV cases declined from 225 in 2003 to 134 in 2004, the lowest incidence of polio in India since the polio eradication initiative began.

As of June 18, 2005, India reported 18 polio cases with paralysis onset dates during January-May 2005, compared with 13 cases reported for the same period in 2004. Despite this apparent increase, substantial evidence exists to indicate continued restriction of WPV transmission. First, AFP surveillance sensitivity has improved substantially since mid-2004, particularly in Bihar and Uttar Pradesh. Second, genetic-sequencing data indicate that transmission is substantially restricted, with only two P1 genetic clusters circulating in 2005 (as of June 18). Third, P3 was last isolated in December 2004. Analysis of surveillance data through the remainder of 2005 will indicate whether P3 has been eliminated. Finally, the geographic distribution of P1 circulation has been less extensive during the first 5 months of 2005 compared with the same period in 2004, when cases were identified in the southern states of Karnataka and Tamil Nadu.

The polio laboratory network remains one of the strongest components of India's polio eradication program. The laboratories provided rapid results in 2004, even though more than twice as many specimens were tested that year as in 2003. Genetic data provided by ERC are being used to target efforts in the most critical areas. For example, during SIAs, vaccinators are now deployed along major train routes because genetic data and epidemiologic case investigations have identified routes of virus transmission across districts and states.

Throughout 2004 and the first 6 months of 2005, innovative strategies were used to increase the efficiency of SIAs. Through intensive cooperation among GOI and partner agencies, mOP1 was rapidly developed, licensed, and made available to the polio eradication program. Emphasis on community education that targets specific subpopulations and children in transit, as well as enhanced collaboration among all polio eradication partners, will help ensure that children in populations at highest risk are reached. Combining a more effective vaccine with improvements in its delivery increases the likelihood of interrupting WPV transmission.

The reduced number of polio cases, reduced genetic diversity, and geographic spread of the virus, increased surveillance sensitivity, and improved SIA quality suggest that India will soon eliminate poliovirus. Success depends on the continued involvement of state and national governments, in collaboration with polio eradication partners.

* Mass campaigns conducted during a brief period (days to weeks) in which 1 dose of oral polio vaccine (OPV) is administered to all children aged <5 years, regardless of vaccination history. The geographic extent of campaigns (national versus subnational) is determined by analysis of surveillance data. OPV can be administered at fixed sites, by mobile teams during house-to-house visits, by mobile teams at transit points (e.g., train stations or markets), or through a combination of strategies, depending on local circumstances.

([dagger]) Two specimens collected [greater than or equal to] 24 hours apart, both within 14 days of paralysis onset, and shipped on ice or frozen ice packs to a WHO-accredited laboratory.

([section]) Includes eight regional coordinators, 21 subregional coordinators, and 265 district-level SMOs.

([paragraph]) Isolates within a cluster share [greater than or equal to] 95% VP1 nucleotide sequence identity.

References

(1.) CDC. Progress toward global eradication of poliomyelitis, 2002. MMWR 2002;52:366-9.

(2.) CDC. Progress toward poliomyelitis eradication--India, 2002. MMWR 2003;52:172-5

(3.) CDC. Progress toward poliomyelitis eradication--India, 2003. MMWR 2004;53:238-41.

(4.) India Expert Advisory Group. Conclusions and recommendations: the Twelfth Meeting of the India Expert Advisory Group for Polio Eradication, New Delhi, India, 2-3 December 2004. New Delhi, India: National Polio Surveillance Project. Available at http://www.npspindia.org/advisory.asp.

(5.) John TJ, Devarajan LV, Balasubramanyan A. Immunization in India with trivalent and monovalent oral poliovirus vaccines of enhanced potency. Bull World Health Organ 1976;54:115-7.

(6.) Caceres VM, Sutter RW. Sabin monovalent oral polio vaccines: review of past experiences and their potential use after polio eradication. Clin Infect Dis 2001;33:531-41.

(7.) Roberts L. Infectious disease. Polio eradication effort adds new weapon to its armory. Science 2005;307:190.

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, New Delhi; Poliovirus Laboratory Network, Ahmedabad, Bangalore, Chennai, Coonoor, Kasauli, Kolkata, Lucknow, and Mumbai; UNICEF, New Delhi, India. Vaccines and Biological Dept, WHO, Geneva, Switzerland. Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Global Immunization Div, National Immunization Program, CDC.

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