Trouble spots remain in goal toward poliovirus elimination

Polio cases worldwide reached historic lows in 2012, and Pakistan, Nigeria and Afghanistan are the only countries where polio remains endemic, according to results presented during the annual meeting of the American Society of Tropical Medicine and Hygiene.

Through October, just 177 polio cases were reported worldwide for the year, which represents a drop from 502 during the same period last year. However, experts said challenges remain. For example, many parents in Pakistan refuse to vaccinate their children, and in Nigeria, polio cases more than doubled in 2012. This increase in cases could threaten the status of surrounding countries that are currently polio-free, according to a press release from the ASTMH.

Steven Wassilak, MD, a medical epidemiologist and polio expert at the CDC, said during his presentation that new data from Pakistan indicate wild poliovirus type 3, one of the two types of wild poliovirus circulating in the country, is close to being eliminated.

“There have not been any type 3 cases reported for 6 months, which is the longest gap in incidence there to date,” he said in an ASTMH press release. “CDC works with Pakistan officials to monitor different chains of transmission over time, and type 3 is now down to only one chain, which is an indication that we are close to breaking the last link of type 3.”

Barrier to polio elimination

Anita Zaidi, MD, a pediatrician at Aga Khan University in Karachi, who serves on Pakistan’s National Immunization Technical Advisory Group, said Pakistan has made major progress against polio by expanding immunization campaigns, but the remaining challenge is not one easily solved by additional resources.

Anita Zaidi

“We found that, in Karachi, a key reason children fail to get immunizations is not due to lack of access, but because their parents refuse to participate,” Zaidi said in a press release. “That is a big challenge and not something that can be overcome only by expanding immunization campaigns.”

Zaidi and colleagues reported that, in Karachi, “parent refusal was the most common reason given for the failure of children to participate in two recent polio supplementary immunization activities,” accounting for 74% of missed immunizations. These findings were reported in a recent Bulletin of the World Health Organization.

Given the current volatile environment and continued evidence of widespread viral transmission in sewage sampling, Zaidi said Pakistan is making considerable progress in reducing polio cases, but eradication by 2013 appears unrealistic.

“Efforts should focus on building trust through grassroots efforts using community elders in populations with high vaccine refusal rates,” she said. “By providing vaccination at mass transit sites such as bus routes used to travel up-country throughout the year, we can at least isolate the viral reservoirs and make sure we avoid what happened last year, which was exporting the virus to China.”

Rising cases in Nigeria

Opposition to poliovirus immunization is also a major challenge in Nigeria, where the number of polio cases has risen for the second straight year, according to Adamu Nuhu, MD, of Nigeria’s National Primary Healthcare Development Agency. He said cases are mostly confined to the North.

“We are working now with traditional leaders in the North who are respected by local people to change the perceptions of polio immunization and encourage more participation in immunization efforts,” he said in a press release. “There is evidence that overall, immunization rates among children at risk are rising to 80%.”

Nuhu described a campaign under way that involves going house-to-house to identify family decision-makers and discuss with them about the importance of polio immunization. Health officials are also working closely with international partners to pursue new strategies to improve immunization coverage in nomadic groups.

Experts have said the persistence of polio in Nigeria — where there were 99 documented cases in 2012 — is especially worrisome because cases in Nigeria have spread in the past to Sudan, Chad and 23 other countries. All of these countries are now once again polio-free, except for Chad. The CDC reported in October that Chad could interrupt wild polio transmission by the end of this year, but failure to stop transmission in Nigeria could prompt new outbreaks.

For more information:

Wassilak S. #92. Presented at: ASTMH 61st Annual Meeting; Nov. 11-15, 2012; Atlanta.