'An intense schedule of mass vaccination in the endemic states of Uttar Pradesh, Bihar and other high risk areas has resulted in a rapid decline in polio cases in India,' Hamid Jafari, project manager of WHO National Polio Surveillance Project, told IANS.

Caused by a virus that invades the nervous system, polio paralyses the nervous system within a few hours of infection. Children below the age of five are susceptible to the disease.

The spread of the virus gathers momentum with person-to-person contact, unhygienic surroundings, and drinking unclean water. The illness could last for 2 weeks, but can cause irreparable damage to the nerves in some cases.

Poliomyelitis virus is classified into Type 1, 2 and 3. Type 1 and Type 3 continue to be a challenge in parts of Afghanistan and Africa, while Type 2 has been eliminated.

'When the virus infects a person, it enters the bloodstream and then settles in the spinal cord and brain, producing paralytic poliomyelitis. It renders the affected limb useless,' said Deepak Ugra, president of Indian Academy of Pediatrics (IAP).

'The burden is immense, as the patient leads a crippled life, and the whole family is affected,' added Ugra.

Uttar Pradesh and central Bihar, with their hard to reach populations in the Kosi river area, have not reported Type 1 polio since November 2009.

Importantly, this is the lowest ever level of reported cases during the peak transmission season, which extends from July through September. Nearly all of it is outside Uttar Pradesh and Bihar, Jafari adds.

'Building on immunisation campaigns, the introduction of bivalent vaccine in early 2010 has enabled concurrent control of both Type 1 and Type 3 polio virus,' said Jafari.

Under the Global Polio Eradication Initiative (GPEI), central and state governments, WHO, Rotary International, and the United Nations (UN) are fast working towards eradicating the disease totally.

The Ministry of health and WHO have also been working on the national polio surveillance project, monitoring the status of acute flaccid paralysis (AFP) in India.

The recent cases of polio transmission have been reported in Murshidabad (West Bengal) and the adjoining district of Pakur (Jharkhand), Nasik and Beed districts of Maharashtra, and East Champaran district of Bihar, close to a polio infected district of Nepal.

On the global front, Pakistan has reported more cases than the other three endemic countries combined (88 compared to 65). Of the 113 districts affected by polio worldwide in the past six months, 20 percent are in Pakistan.

While India has been largely dependent on oral polio vaccine (OPV) strategy, experts now root for a change in vaccination strategy.

'A strategy shift from OPV to injectable polio vaccine (IPV) will avoid problems such as vaccine-associated polio, risk of polio in immune-compromised children and risk of vaccine-derived polio outbreaks' said T. Jacob John, member of the Global Advisory Polio Eradication Committee, WHO.

OPV is a live but weakened virus given as drops to children.

However, most developed countries have already switched to IPV which contains killed or inactivated virus.

A nation is declared polio-free when there are no cases reported for three consecutive years, according to WHO guidelines.

'The priority is to stop the transmission of polio through vaccination in and around polio affected districts,' said Jafari.

The number of polio cases in India has been declining over the past few years, except for a sudden spurt last year. In 2006, the country reported 676 polio cases, which declined to 281 the following year. The number of cases was 449 in 2008, and 741 in 2009.

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