1. A vaccine against enterovirus 71 (EV71) provided protection against hand, foot, and mouth disease (HFMD) in infants and children between 6 to 35 months of age.
2. Subgroup analysis demonstrated that a neutralizing antibody titer of 1:16 or greater was associated with adequate protection against EV71 HFMD and herpangina.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Hand, foot, and mouth disease (HFMD) is a common childhood infection, caused by an enterovirus (EV71) or coxsackie (A16) virus, which can lead to serious neurologic consequences. Transmission occurs through close contact by the fecal-oral route and symptoms range from skin lesions to aseptic meningitis or severe encephalitis. This randomized, controlled trial examined the efficacy and safety of a new inactivated vaccine developed against EV71.
The EV71 vaccine reduced the number of cases of all EV71-associated diseases (HFMD, herpangina, and neurologic complications of HFMD) with a protective efficacy of 89.3% and 88.0% at 6 months and 1 year, respectively. However, this vaccine did not provide cross-protection against coxsackie A16 and the overall incidence of HFMD was not reduced. Similar rates of adverse events were reported in the vaccine and placebo groups. Antibody titers to EV71 were followed in a subgroup of both vaccinated and placebo groups. In the vaccinated group, the titers remained steady up to 14 months. A titer of 1:16 had the greatest sensitivity and specificity for disease protection.
Given the endemic nature of EV71 infections and the various genotypes of this virus, results of this study may only be generalizable to the region where this study was conducted. Furthermore, seropositivity for EV71 antibodies was not evaluated at baseline for all patients and so it was assumed that these patients were evenly distributed between the two groups. Nevertheless, this new vaccine is a promising step towards eventual eradication of another common condition with significant morbidity and mortality. Future studies are needed to determine the duration of this vaccine’s efficacy.
In-Depth [randomized, controlled, phase 3 trial]: This was a double-blinded, randomized, controlled trial that included infants and children between 6 to 35 months of age. Patients were either given the vaccine (n=4719) or placebo (n=4711) and all were followed at regular intervals. Parents were instructed to take their children to specific hospitals for any illness during the study period. The primary end point was the occurrence of HFMD or herpangina. The incidence density of EV71-associated HFMD or herpangina at 1 year was 1.0 cases/1000 person-years in the vaccine group compared to 19.3 cases/1000 person-years in the placebo group. The rates of adverse events were similar in both groups (2.2% in vaccine group vs. 2.6% in placebo group).
Of the 1950 cases of HFMD or herpangina reported during this trial, only 99 had confirmed EV71-associated HFMD or herpangina. The subgroup analysis for immunogenicity included 579 patients from the vaccine group and 571 patients from the placebo group. Among the vaccine and placebo groups, 92.4% and 25.3% had antibody titers greater than 1:16 at 14 months, respectively. All 11 cases of EV71-associated HFMD or herpangina in this subgroup analysis were also noted to only be from the placebo subgroup.
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