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1. An outbreak of imported polio virus in China was stopped within 1.5 months of the index case with increased surveillance and five rounds of supplementary immunization.
Study Rundown: Twenty-one cases of infection with poliovirus type 1 were identified in the Xinjiang region of China between July 3 and October 9, 2011. China was declared a poliomyelitis-free region in 2000, and genetic sequencing data suggested that the virus was imported from Pakistan.
The incidence of poliovirus infection in this outbreak was highest among children, especially those under 1 year of age (3.46 per 100,000). However, almost half of the cases involved people between 15 and 39 years of age (0.22 per 100,000). Supplementary vaccination was initially aimed at children under 15, but coverage was expanded to all persons under 40 once adult cases were identified. In all, 43.7 million doses of vaccine were administered.
Vaccine coverage in Xinjiang prior to the outbreak was considered low relative to other regions of China. In a sample of 2611 healthy persons of any age in southern Xinjiang, 90.4% had antibodies against poliovirus. Among children younger than 5 in the sample, only 80 to 92% had antibodies. After the first three rounds of supplementary immunization, 97.8 to 99.3% of people sampled were positive for antibodies against poliovirus, and had higher antibody titers on average than before.
Supplementary immunization was carried out using both the trivalent oral polio vaccine (OPV) and the monovalent OPV type 1 (OPV1). A 2007 study showed that the monovalent OPV1 is more effective per dose than the trivalent OPV. Thus, the monovalent OPV1 is thought to facilitate a more rapid response in the setting of an outbreak.
Although successful in this case, outbreak response is a costly endeavor that requires significant infrastructure and expertise. Not all countries are as well-equipped as China for an outbreak. Without global eradication of poliovirus, all countries continue to be at risk. Economic analyses suggest that eradication, while costly in the short-term, would ultimately cost less than a policy of control without eradication.
Click to read the study, published today in NEJM
Click to read an accompanying editorial in NEJM
Relevant Reading: Eradication versus control for poliomyelitis: an economic analysis; Poliomyelitis Prevention: Recommendations for Use of Inactivated Poliovirus Vaccine and Live Oral Poliovirus Vaccine
By Tomi Jun and Adrienne Cheung
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