The number of polio cases in 2007 declined in Afghanistan and Pakistan, two of the last countries where transmission has never been interrupted. But security and operational problems remain significant barriers to stopping transmission, according to a recent report by the international polio eradication partnership.

The March 28 issue of Morbidity and Mortality Weekly Report from the U.S. Centers for Disease Control and Prevention reports that Afghanistan had 17 cases in 2007, down from 31 in 2006. Pakistan had 32 polio cases in 2007, compared to 40 in 2006.

Polio transmission continued in regions where significant numbers of children were not fully vaccinated. These regions include remote border areas of both countries, where security concerns have hampered vaccination efforts. In a breakthrough in August 2007, anti-government forces in Afghanistan agreed to support vaccination campaigns.

Security was not the only factor contributing to the spread of polio in Pakistan, though. Vaccination campaigns in some relatively secure southern districts also missed significant numbers of children and had several polio cases as a result.

Most of the 2007 vaccination campaigns targeted the more virulent type 1 virus with monovalent vaccine, alone or in addition to trivalent vaccine. The proportion of cases caused by type 1 virus declined in Afghanistan between 2006 and 2007, from 94 percent to 35 percent, but increased slightly in Pakistan, from 50 percent to 59 percent.

The report described progress against polio as “limited,” and said improvements in security, as well as the quality of vaccination campaigns in secure areas, will be needed to eradicate the disease.

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