Poor vaccine uptake blamed for polio rise in Pakistan, Afghanistan

By Helen Albert

The number of cases of poliomyelitis per year in Pakistan and Afghanistan has more than doubled since 2006 despite improvements in available vaccine efficacy, show study findings in The Lancet.

The researchers found that there was a correlation between vaccine coverage and number of cases, with areas with the worst vaccine uptake being the most badly affected.

"The new vaccines appear to be more effective than the trivalent vaccine, which offers encouragement that polio eradication is achievable," commented Kathleen O'Reilly (Imperial College London, UK) in a press statement.

"But the best vaccine in the world will not work unless it reaches the children its intended to protect. So it's vitally important that vaccine coverage is considerably improved in 2012 through better campaigns and routine programmes if we're to finally eradicate polio globally," she added.

To assess how effective the newer mono- and bivalent oral poliovirus vaccines are at protecting children from the virus in comparison to the older trivalent vaccine, O'Reilly and colleagues carried out a matched case-control study from a database of 46,977 children (aged 0-14 years) who experienced flaccid paralysis between January 2001 and December 2011 from a variety of causes.

The team compared the vaccination history of children with paralysis due to polio with those who experienced paralysis for other reasons.

In total, 883 cases of poliomyelitis serotype 1 (710 in Pakistan; 173 in Afghanistan) and 272 cases of poliomyelitis serotype 3 (216 in Pakistan; 56 in Afghanistan) occurred during the study period.

The researchers found that the mono- and bivalent vaccines were significantly more effective against poliomyelitis serotype 1 than the trivalent vaccine, with estimated clinical efficacies of 34.5% and 23.4%, respectively, compared with 12.5%. There were not enough cases of poliomyelitis serotype 3 over this period to accurately assess vaccine efficacy.

O'Reilly and colleagues found that there was a significant association between lower vaccine uptake from 2006 onwards and having a higher number of cases in 2011, particularly in Balochistan province, Khyber Pakhtunkhwa province, and the Federally Administered Tribal Areas in Pakistan and in southern Afghanistan.

There was also a significant negative correlation between ranked population immunity against poliomyelitis serotype 1 and incidence in each district, consistent with lack of vaccine uptake being responsible for the observed increase in incidence of the disease.

"Vaccination coverage must be considerably improved in 2012 through higher quality campaigns and routine programmes if global eradication of poliomyelitis is to be achieved," conclude the authors.

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