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India is no longer a polio-endemic country

On the evening of Thursday 23 February 2012, the Tower of London, UK, was emblazoned with a series of projections highlighting Rotary Day, a celebration of the founding of the charitable organization Rotary International more than 100 years ago. The images focused on Rotary International's End Polio Now Campaign, which, under various different titles, has been the organization's flagship fundraising campaign for more than 20 years. In addition to raising public awareness of the campaign, the display was arranged in anticipation of an exciting announcement, which came two days later, when the WHO declared that India is no longer a polio-endemic country.

Polio is caused by infection with poliovirus, a positive-strand RNA virus that belongs to the Picornaviridae. As an enterovirus, poliovirus is transmitted by the faecal–oral route and can replicate in the intestine. Most poliovirus infections are asymptomatic, but in roughly 1% of cases the virus spreads from the intestine to the central nervous system to infect the anterior motor neurons that innervate the muscles, causing paralysis. An estimated 5–10% of individuals with paralytic disease die from respiratory paralysis, ∼10% make a full recovery and the remainder recover some limb function but can be left with a debilitating disability.

Although records show that polio is an ancient disease, it was not a major public health problem until the mid twentieth century, when it was one of the most feared infectious diseases in developed countries. The development of the inactivated polio vaccine by Jonas Salk and the oral polio vaccine (OPV) by Albert Sabin in the late 1950s and early 1960s, respectively, quickly led to the disease being controlled in developed countries, and by the mid 1970s polio had been eradicated from most of Europe and North America. In developing countries, however, the disease was neglected, and in 1988 there were an estimated 350,000 cases in 125 countries worldwide. Following the success of mass OPV immunization campaigns in South America, the Global Polio Eradication Initiative (GPEI) was launched by the World Health Assembly in 1988, with the aim of eradicating the disease by 2000 through immunization with OPV.

Twenty four years — and >US$9 billion — later, that aim has yet to be achieved. Great strides have been made; by 2000, polio was endemic in just a handful of countries, and the annual number of polio cases had decreased by ∼99%. Over the next decade, however, the programme underwent a series of setbacks, with imported wild poliovirus or, in some cases, vaccine-derived virus causing major outbreaks in countries that had previously been free of the disease. Such problems are still ongoing, and although there are now only three polio-endemic countries — Afghanistan, Pakistan and Nigeria — persistent transmission has been re-established in Angola, Chad and the Democratic Republic of the Congo, and there are ongoing outbreaks due to imported virus in at least ten other countries, including China, Kenya and Nepal.

The programme has evolved in response to the challenges it has faced, and in 2010 a new strategic plan was implemented, which set the goal of stopping polio transmission in two of the four endemic countries by the end of 2011 and stopping transmission completely by the end of 2012. Crucially, an Independent Monitoring Board (IMB) was also established to monitor progress, and it has been frank in its assessments. The latest IMB report, Ten Months and Counting , contains some stark warnings. Although the success in India is rightfully lauded, with praise for its “outstanding public health leadership” and “unswerving political commitment”, the report also highlights the fact that in 2011 the number of polio cases in the three remaining endemic countries increased. The situation in specific areas of Nigeria and Pakistan in particular is giving grave cause for concern. In Nigeria, the number of recorded polio cases in 2010 fell by 95% compared with the previous year, but the programme failed to build on this success, and there was no increase in vaccine coverage last year; the report notes that, in 2011, “Nigeria's performance plummeted to unacceptable levels”. Pakistan accounted for 30% of all recorded polio cases in 2011, and although the report praises the emergency plan now in place as being “considerably stronger” than before, it also notes that as yet this plan has made “no demonstrable impact on transmission”.

The IMB concludes that there are only two outcomes for the eradication programme: success or failure. The recent success in India, if it can be maintained, could act as an effective springboard for the final push to tackle the last remaining outposts of polio in the world. As long as polio is present in one country, the rest of the world is at risk; ignoring the 1% is not an option.