Dr. Surendran, Surveillance Medical Officer*
National Polio Surveillance Project, World Health Organization.*
"All interest in disease and death is only another expression of interest in life" - Thomas Mann.

Surveillance is the backbone of public health programme and provides information so that effective action is taken in controlling and preventing diseases of public health importance.(1) Surveillance is defined as the ongoing systematic collection, correlation, analysis and interpretation of data and dissemination of information to those who need to know in order that action is taken. VPD surveillance is essentially state based surveillance programme in the country.
  • To detect clustering of cases to trigger interventions to prevent transmission.
  • To assess public health impact of health events and determine their trends.
  • To demonstrate need for public health intervention programmes and resources and allocate resources during public health planning.
  • To monitor effectiveness of prevention and control measures.
  • To identify high risk groups/geographical areas to target interventions.

The impact of immunization programme is assessed in terms of Vaccine Preventable Diseases (VPD) magnitude (Figure 1) and mortality.

Polio incidence had declined from 24,000 reported cases in 1988 to 283 cases (as on 8th September '06) in 2006. (Figure 2) The transmission continues to be endemic predominantly in Western UP and to a lesser extent in Bihar. The ongoing outbreak in Western UP, is spreading to the other states. Most states in India have become polio-free.

Most polio transmission is due to P1 serotype and to a lesser extent of P3 serotype, (Figure 3). The last wild polio virus type II transmission was documented in Aligarh (Western Uttar Pradesh, India) in 1999 at global level and it is presumed that wild polio type II transmission had been interrupted.

Three doses of trivalent oral polio vaccine (t-OPV) elicit 95% vaccine efficacy in temperate countries. Review of data from developing countries showed t-OPV produces sero-conversion rate of 73% of type I, 90% for type II and 70% of type III. This low sero-conversion may be due to recurrent diarrheal infections, malnutrition and other factors2.

Over two thirds of polio cases occur among children less than 2 years of age. However, 1-3% of polio cases occur among children over 5 years of age (Figure 4). Males are more affected than females (Figure 5). Muslim community has a higher incidence of poliomyelitis compared to Hindu community due to poor vaccination practices prevalent (Figure 6). Polio is a seasonal disease with peak incidence during July-October in India. National Immunization Days are scheduled during low transmission period Feb-May (Figure 7).

Measles is a seasonal disease. Measles epidemics in India are more common in winter and early spring (Jan-Apr). Introduction of effective measles vaccine since 1985, has altered the epidemiology of measles. The reported measles immunization coverage is approximately 90.3% during 2004-05. However, the evaluated coverage shows 20-40% lesser than the reported coverage (Figure 8). As the measles coverage increased, there has been a marked reduction in measles incidence and there is a shift to higher age group. More than 50% of cases reported in India, is found among under 5 years of age, indicating poor measles vaccination coverage. Outbreaks generally occur due to accumulation of measles susceptible population among both unvaccinated children and the vaccinated but primary vaccination failure children. Prior to 1985, outbreaks occurred at an interval of about three years, after introduction of measles vaccination interval between outbreaks also increased to above 5 years. A review of community based studies of published measles outbreak investigations found a median case fatality ratio of 3.7%. (range 0-23.9%) .(3)
Other VPD Diseases
The DPT3 coverage is 93% during 2004-05. Since 1975, there has been a 72% decline in the incidence of diphtheria and 91% decline in the incidence of whooping cough. The reported diphtheria had shown re-emergence in 2004. The overall tetanus incidence had a significant decline since 1990. There is limited data available on diphtheria, pertussis and tetanus.

Though there is a decline of all the six VPD diseases since 1985, there is a continued under reporting of cases. These reflect inadequate vaccination coverage in some major states of India primarily due to poor planning of immunization delivery services including outreach, man power shortage, little job training/in-service training for health personnel, shortages of vaccine at the point of delivery, weak supervision and monitoring.(4)

The VPD surveillance data reflected recorded cases and deaths in the out-patient and in-patient departments of hospitals, dispensaries, CHC, PHC and other health facilities.(5) These aggregated data is sent to the district on monthly basis which in turn aggregated at the state and national level. It is presumed that there is significant under reporting of VPD diseases. The AFP surveillance networking for polio had been an excellent functional model since 1997 to add other diseases. Based on the proven success, there are serious considerations to include other VPD diseases for disease surveillance. Govt. of India had initiated integrated measles with AFP surveillance in the states of Tamil Nadu, Karnataka and Andhra Pradesh. The other states will be integrated at a later date in a phased manner.

Nationally there is inadequate disease surveillance system and the data that is generated is not used for immediate action purposes. Any control or elimination or eradication programme would depend on availability of good quality surveillance data at the national, state and district level.(6) With the currently prevalent system it will be difficult to assess the true burden of disease.

There are many vertical disease programmes to facilitate rapid response. A fragmented approach to disease surveillance results in costly and inefficient duplication of effort, and therefore integrated disease surveillance system will overcome the above limitation. Immunization services can also be the victims of their own success when planners use disease surveillance data for the basis for budget allocation.(6)

References :
  1. Integrated Disease Surveillance Project Training Manual - GOI - 2006.
  2. Surveillance of Acute Flaccid Paralysis Field Guide 3rd Edition Sept 2005 MOH & FW GOI.
  3. Measles Mortality Reduction - India strategic plan 2005-2010 Nov. 2005 MOH & FW, GOI.
  4. Universal Immunization Programme Multi year strategic plan 2005-2010 Jan 2005 MOH & FW, GOI.
  5. Immunization essentials - A Practical Field Guide 2003 USAID.
  6. Immunization practice - A Practical Guide for Health Staff 2004 (WHO).
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