POLIOMYELITIS, a paralysing disease that used to strike as many as 600,000 children each year, is fast disappearing from almost all over the globe but the Indian subcontinent remains vulnerable, warns the World Health Organisation (WHO).

In the Western hemisphere, the last case of paralytic polio was reported over 2 years ago and the disease is on its way out in North Africa, the Middle East, China and the Pacific, according to WHO experts. But the Indian subcontinent is a major reservoir for wild polio viruses, and they say that efforts must be directed towards eradicating this disease here.

A recent issue of the British journal The Lancet (Vol 343, No 8909), reports that Harry F Hull of the WHO's Extended Programme on Immunisation (EPI), and his colleagues as saying that if epidemics in the developing world can be checked, industrialised countries will also be able to save large sums they spend annually on polio vaccines. The World Bank estimates that the global eradication of poliomyelitis would save more than $300 million annually in the US alone.

With the development of the Salk inactivated polio vaccine (IPV) as early as 1955 and the Sabin oral polio vaccine (OPV) in 1961, the eradication of this disease became technically possible. In 1992, the number of polio cases recorded in 131 of the 211 countries reporting to the WHO was nil.

The eradication of polio in the Western hemisphere was possible largely due to the efforts of the Pan American Health Organisation. The last chains of transmission of this disease were broken when more than 3.8 million doses of OPV were administered from house to house in coastal Colombia and northern Peru.

Experts say that the spread of this disease is now highly localised. In 1992, 64 per cent of the polio cases reported were from the Indian subcontinent and several thousand cases were reported from China and several other countries in southeast Asia. Polio remains poorly controlled in Pakistan, while in Bangladesh and Nepal, eradication activities are only beginning.

In India, the Union ministry of health and family welfare claims that 85 per cent of the children below 5 years of age -- over 110 million -- were immunised against polio in 1990-91. However, concerns have been raised about the increasing number of polio cases among children who have received the required 3 doses of the OPV.

Says Usha Saxena, a member of the Indian Academy of Paediatricians, "High immunisation coverage does not imply that the disease has been controlled." She attributes the poor control to a breakdown in the cold chain -- the system in place to ensure that vaccines are maintained at appropriate temperatures, which are necessary if they are to be effective -- particularly in rural areas, where they are often placed on ice to keep them cold. She also points out that the uptake of the OPV in the tropics is affected by the presence of enteroviruses -- viruses that infect the intestines of children. The injectible IPV, she says, is more effective, as it is unaffected by enteroviruses. However, IPV has to be imported and is expensive.

The WHO estimates that global polio eradication over a 10-year period may cost as much as $1,000 million. Although several experts claim that the IPV may be more effective in immunising children, Hull points out, "Most polio cases in endemic countries occur today amongst unimmunised children and eradication must be achieved by improving vaccine delivery, rather than by altering immunisation schedules."