February 18, 2014
2 min read

Incidence of VAPP in Latin America, Caribbean lower than estimated

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Researchers with the Pan American Health Organization/WHO have found that the incidence of vaccine-associated paralytic poliomyelitis in Latin American and Caribbean countries is lower than previously estimated, according to a report in The Journal of Infectious Diseases.

The researchers used data from the Latin America and Caribbean surveillance system for acute flaccid paralysis (AFP). From 1992 to 2011, the average AFP rate in Latin America and the Caribbean was 1.35 cases per 100,000 children younger than 15 years. Cases are entered into the Polio Eradication Surveillance System and Integrated Surveillance Information System, both maintained by the Pan American Health Organization. These data were used to identify cases of vaccine-associated paralytic poliomyelitis (VAPP).

During the study period, there were 40,926 cases of AFP in Latin America and the Caribbean, of which 526 (1%) had no clinical information and 19,902 (49%) had no residual paralysis and were excluded from the analysis. Another 6,751 cases (16%) had residual paralysis 60 days after onset of paralysis and 13,747 (33%) had unknown status of residual paralysis. Among all cases, 23,634 (58%) had a documented date of receipt of the oral polio vaccine. In the field, there were 72 cases of VAPP diagnosed.

Among the 6,751 cases of residual paralysis, 209 had vaccine-strain poliovirus isolated from their specimens. Sixty-two were excluded. Of the remaining 147 cases, 41 occurred in the 4- to 40-day interval from vaccination to paralysis onset. The 106 remaining cases were classified as nonrecipient VAPP.

Among the cases with an unknown status of residual paralysis, 251 had a vaccine strain poliovirus isolated from their specimens. Among these, 117 were excluded. Of the remaining 134 cases, 31 occurred in the 4- to 40-day interval from vaccination to paralysis onset. Thirteen of the cases diagnosed in the field were considered nonrecipient VAPP cases. The remaining 90 cases were excluded.

Overall, there were 72 recipient VAPP cases, for a risk of one case per 3.15 million newborns. There were also 119 cases of nonrecipient VAPP, corresponding with a risk of one case per 1.91 million newborns. The overall risk of VAPP was estimated to be one case per 1.19 million newborns.

“Our findings highlight the importance of assessing the risk of adverse events, particularly one as important as VAPP, in low- and middle-income countries where wild poliovirus has already been eliminated,” the researchers wrote.

Disclosure: The researchers report no relevant financial disclosures.