[NEW DELHI] Crowded conditions and poor hygiene are fuelling India's recurrent outbreaks of polio, hampering global efforts to eradicate the disease.
The findings are reported today (17 November) in Science.
By the end of October this year, 360 people had contracted polio in Uttar Pradesh (UP), north India, compared to just 66 last year. The UP strain has now spread to other Indian states as well as Bangladesh, Nepal and parts of Africa, according to the World Health Organization (WHO).
Now a research team led by Nicholas Grassly of Imperial College London, United Kingdom, suggests that polio transmission in India is linked to high population density and inadequate sanitation — both conditions that boost the likelihood of infectious contact.
"Generally improving sanitation is very important to controlling the spread of not only polio but also enteric [intestinal] diseases," Grassly told SciDev.Net.
"It is an important public health priority, but may take longer to achieve in India than the currently envisaged window for polio eradication."
According to the Indian government, the WHO and UNICEF, the UP outbreak was caused by gaps in immunisation coverage.
But Grassly's team are challenging this conclusion.
They say that children in UP have received far more doses of vaccine than those in the rest of India and other endemic countries. By the end of 2005, children under five in UP and neighbouring Bihar state received on average almost 15 doses of the oral polio vaccine, compared to ten for children of the same age in the rest of India.
The problem is not the vaccine's quality, say the researchers, but its efficacy — they estimate it to be just nine per cent effective, compared to 21 per cent elsewhere in India.
They say the lower efficacy observed in UP must be due to serious environmental problems — UP is India's most populous state and has one of the worst infrastructures and sanitation records.
Grassly and his colleagues analysed more than 96,000 cases of paralysis caused by the polio virus since 1997 and prepared computer models to track infection rates.
The new findings are consistent with observations by T. Jacob John, a member of India's national advisory board on polio, who found that the oral polio vaccine is less effective in India than in the West.
John told SciDev.Net that although more research is needed in the field, part of the problem could be due to the prevalence of intestinal viruses and diarrhoea — facilitated by crowding and inadequate sanitation — which cause the vaccine to be washed out of children's bodies.Link to full article in Science
Reference: Science 314, 5802 (2006)