Baby Steps Toward Polio Eradication

Twenty years ago, the WHO pledged to eradicate poliomyelitis. The number of cases decreased by >99% between 1988 and 2005, and wild poliovirus type 2 was eliminated, but eradication has remained elusive. In response to calls for a more immunogenic product, researchers quickly developed a new monovalent type 1 oral poliovirus vaccine. In two recent studies, investigators examined the efficacy of this vaccine in children.

El-Sayed and colleagues conducted a randomized trial involving 421 newborns at three clinics in Egypt. They compared humoral antibody responses after a single dose of monovalent type 1 or trivalent oral poliovirus vaccine administered at birth and quantified mucosal immunity after a challenge dose of monovalent vaccine administered 30 days after birth. They also determined adverse events following vaccination.

Thirty days after vaccine administration, the rate of seroconversion to type 1 virus was higher in the monovalent-vaccine group than in the trivalent-vaccine group (55% vs. 32%; P<0.001). Mucosal immunity also differed between groups: 7 days after monovalent type 1 vaccine challenge, the proportion of participants who were excreting type 1 virus in stool was lower in the monovalent-vaccine group than in the trivalent-vaccine group (26% vs. 42%; P=0.001). Both vaccines were well tolerated; no serious adverse events were attributed to either one.

Using a national surveillance database, Jenkins and colleagues identified cases of virologically confirmed poliomyelitis reported between 2001 and 2007 in Nigerian children aged <15 years. This database also contained information on the types of vaccines and the number of doses administered. The efficacy of monovalent type 1 oral poliovirus vaccine against paralysis from type 1 poliomyelitis was four times that of the trivalent oral vaccine (67% [95% confidence interval, 39–82] vs. 16% [95% CI, 10–21]).