The massive effort to eradicate polio through worldwide vaccination hit some new speed bumps over the past several days, with fresh reports of outbreaks of the disease in the Horn of Africa, and continued deadly attacks on polio workers in rebel-controlled areas of Pakistan and Nigeria.
Nevertheless, the overall outlook for eradication of polio remains highly promising.
The campaign entered a pivotal and potentially decisive phase last month with the launch of a $5.5 billion strategic roadmap to halt all transmission of wild polio viruses by 2014, and to certify the complete eradication of the disease by the end of 2018. Commitments of $4 billion, including $1.8 billion from the Bill & Melinda Gates Foundation, were announced at an April 25 vaccine summit in Abu Dhabi.
The new plan, formally named the Polio Eradication and Endgame Strategic Plan: 2013-2018, was developed by the Global Polio Eradication Initiative and its partners with support from The Boston Consulting Group. The plan has been endorsed by over 400 leading scientists in a statement declaring the eradication of polio to be “an urgent and achievable global health priority.”
Viewed from one perspective, a successful outcome to the 25-year polio campaign seems close at hand: worldwide cases of paralytic polio, which stood at 350,000 in 1988, fell to an all-time low of 223 in 2012. Today, polio remains endemic in only three countries (Pakistan, Afghanistan, and Nigeria), down from 125 countries in 1988.
And yet, while wiping out the polio virus is an eminently achievable proposition,
the final stage of the effort presents complex, difficult challenges. As Bill Gates stated in his Dimbleby Lecture in London in January, “the last mile is not only the hardest mile; it’s also much harder than I expected.”
For one thing, the number of infected persons in 2012 was actually much higher than 223: over 95 percent of people infected with the polio virus are silent carriers who never develop symptoms but can transmit the virus to others through personal contact. The virus also is present sewage in affected areas, and is readily transmitted through exposure to contaminated water used for bathing or drinking.
In addition, remaining reservoirs of the virus are located primarily among extremely hard-to-reach and underserved populations, including nomadic livestock herders, migrant laborers, and people in urban slums. Multiple doses of the vaccine are required to fully immunize a child. Repeatedly reaching these groups is a difficult, labor-intensive task, involving a veritable army of frontline workers and managers.
Upcoming vaccination drives must achieve very high levels of population immunity, ranging between 80-95% depending on local factors. At these levels, each infected person is likely to transmit the virus to less than one additional person, and the number of new infections drops precipitously. Achieving these thresholds, however, is no mean feat.
India, which has not had a new case of polio in over two years, demonstrated the feasibility of accomplishing this task under circumstances of extreme poverty, poor sanitation, and high population density.
India succeeded through a combination of relentless determination and a data-driven, laser-like focus on innovation. Small teams of polio workers visited each household in high-risk areas to track and vaccinate each child. If parents refused, a second team of specially trained “influencers”–local villagers held in high regard–returned to the same household to further explain the value of the polio vaccine. Vaccinators marked each house with chalk, using a code to indicate whether children had been missed. The finger of each vaccinated child was marked with indelible ink to aid in identifying missed children in marketplaces and in transit. In the evening, supervisors reviewed the day’s records, adjusting micro-plans for the following day. Intensive surveillance was conducted to detect new outbreaks, and assets were quickly re-deployed as needed. Every diagnosed case was genetically analyzed to identify where the virus originated.
High immunity levels also must be maintained in countries previously cleared of the virus to guard against its reintroduction by infected travelers. Vigilant monitoring is needed to detect new outbreaks; and programmatic responses to outbreaks must be quick and decisive, with a surge of polio workers deployed to the affected region to conduct emergency vaccination drives. New outbreaks of the disease were reported this month in southern Somalia and eastern Kenya; the Global Polio Eradication Initiative has mounted aggressive vaccination drives in response.
The ultimate wild card in the eradication effort is political instability and violence in rebel-controlled areas of the three endemic countries. Since December, scores of polio workers in Pakistan, Afghanistan and Nigeria have lost their lives in targeted assassinations in high-risk areas. Security arrangements have been beefed up, but violent incidents are continuing and the short-term outlook remains uncertain. If needed, the campaign will conduct intensive vaccination drives in surrounding areas, including vaccination of travelers moving in and out of affected areas, to hold onto gains and buy time.
Looking beyond current political obstacles, the outlook is highly promising. India has demonstrated that greatly-detailed vaccination campaigns covering vast populations can be executed with exquisite precision by carefully-selected, well-trained and properly supervised health workers. The lessons derived from India’s experience have been incorporated into the new strategic plan, and India’s technical advisors are assisting the remaining endemic countries in executing their national plans.
It is India’s dramatic achievement that has catapulted polio eradication to the top of the near-term global health agenda. The “last mile” to eradication may be hazardous to transverse–but the end-point is now in sight. Ultimate victory against polio means that no child will ever again be struck down by this devastating paralytic disease. A successful outcome also will generate considerable momentum behind other public health initiatives. And the infrastructure developed and lessons-learned from the polio campaign will greatly strengthen these other efforts.