India remains one of the few countries where polio has not been eradicated. Most of the world's new cases are reported in the subcontinent. While the total number of cases dropped in India last year, VOA correspondent Steve Herman reports from New Delhi that one variant of the virus is actually on the increase there.

Indian mothers come out after administering polio drops to their children at hospital in Allahabad, Uttar Pradesh (File)

Most of the cases are in two states. There were nearly 300 cases traced to the P3 virus in Uttar Pradesh and about 140 in neighboring Bihar last year. That compares to fewer than 30 P3 cases in the two states in 2006.

Dr. Devendra Khander is the coordinator of the World Health Organization's polio project in Bihar. He explains why it has been difficult to wipe out the highly infectious disease in those two states.

"The combination of factors, that is, highest population density in India, along with the weak sanitation - in Bihar the flooding is an additional component - a huge group of susceptible children, along with low routine immunization," explained Khander.

Immunization programs in India have focused on the P1 virus, which spreads quickly. The less dangerous P2 strain has been completely eradicated worldwide.

Dr. Khander says, with the decline in P1 cases, the immunization priority will shift to the P3 virus in 2008.

"With this, we should be in a position to finish off the indigenous transmission in Bihar also," said Khander.

But even India's urban environments have not seen an eradication of polio. Two children were diagnosed with the disease last year in New Delhi, although the parents of both say their children had taken oral doses of the vaccine. These are the first cases of P3 viral polio in five years in the Indian capital.

Health officials here say they plan to request the national government to implement a special "pulse" immunization campaign in the capital. This would involve a mass, simultaneous immunization targeting children up to five years old.

Polio spreads mainly among young children through contaminated food or water. It is considered to have been wiped out in most of the world, except in Nigeria, Afghanistan, India and Pakistan.