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Additional targeted interventions urged to interrupt polio transmission
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Decreases in vaccination coverage with poliovirus vaccine led to increases in poliomyelitis in Pakistan and Afghanistan, and more efforts are needed, according to study findings published online.
Kathleen M. O’Reilly, PhD, research associate in the School of Public Health at the Imperial College in London, and colleagues performed a case-control analysis based on a database that included nearly 47,000 children aged 0 to 14 years who had acute flaccid paralysis onset between January 2001 and December 2011. The researchers aimed to establish why incidence is rising in these countries, even though innovations, including the introduction of new vaccines, have been implemented.
Overall, the researchers reported that 710 children had serotype 1 poliomyelitis in Pakistan and 173 in Afghanistan; 216 children were found to have serotype 3 in Pakistan and 56 in Afghanistan.
The researchers said the monovalent and bivalent formulations of oral poliovirus vaccine (OPV) showed similar results, with effectiveness rates at 34.5% for monovalent and 23.4% for bivalent. The trivalent was about 12.5%, according to the study data.
“The effectiveness of bivalent OPV is comparable with monovalent OPV and can therefore be used in eradicating serotype 1 poliomyelitis and also minimize the risks of serotype 3 outbreaks. However, decreases in vaccination coverage in parts of Pakistan and southern Afghanistan have severely limited the effect of this vaccine,” the study researchers concluded.
The researchers also said armed conflict and safety concerns remain major challenges to vaccination campaigns and routine health and immunization services.
“We noted that access to routine immunization decreased in Balochistan and FATA [Federally Administered Tribal Areas] in Pakistan, with just 25% to 33% of children under 3 years old reported to have received three or more doses of OPV through routine services. … This finding contrasts with improvements in routine immunization coverage in areas free from conflict,” the researchers wrote.
In an accompanying editorial, Philip D. Minor, PhD, of the Division of Virology, National Institute of Biological Standards and Control, in South Mimms, United Kingdom, said “use of suitable vaccines given appropriately is key to the eradication of the last cases attributable to wild type poliovirus.”
Pakistan and Afghanistan are two of the three remaining countries that have yet to interrupt wild-type poliovirus transmission.
Disclosure: The researchers report no relevant financial disclosures.
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