Two doses of an enterovirus 71 vaccine had an efficacy of 80% against EV71-associated disease in Chinese children.
Enterovirus 71 (EV71) is associated with hand, foot, and mouth disease (HFMD) and other, more-serious conditions. Infants and young children are most affected; epidemics have been especially severe in Asia (JW Infect Dis Jan 30 2013).
Investigators (with partial manufacturer support) recently conducted a multicenter, double-blind, phase III trial of an inactivated alum-adjuvanted EV71 vaccine based on genotype C4, the predominant strain in mainland China. Healthy children in that country, aged 6 to 35 months, were randomized to receive vaccine or placebo (alum adjuvant), administered on days 0 and 28. Of 10,245 enrollees, 96% received both doses.
During active surveillance (from day 56 to month 14), vaccine efficacy in the per-protocol population was 80% against EV71-associated disease and 90% against EV71-associated HFMD. Among 52 participants with laboratory-confirmed EV71-associated disease, 51 were seronegative; all EV71 isolates were genotype C4. Eight placebo-group and no vaccine-group participants were hospitalized for EV71-associated disease. Most participants with clinical HFMD were infected with Coxsackie A virus 16 or other enteroviruses; only 2.1% of episodes were associated with EV71. In the subset studied for immunogenicity, antibody titer was significantly higher in vaccine-group than placebo-group participants. The rate of serious adverse events was similar between groups (1.2% and 1.5%, respectively).
Comment: The authors caution that although EV71 vaccine could help to prevent severe cases of EV71-associated disease, its role in reducing the overall incidence of hand, foot, and mouth disease might be limited because EV71 is only one cause of this syndrome. They also note the need to assess whether the vaccine’s immunogenicity and efficacy are affected by concomitantly administered routine vaccines. Editorialists observe that future studies should examine cross-protection against other genotypes and — because neonatal EV71 infection can be particularly severe — vaccination of infants aged <6 months. Cost-effectiveness analyses can help in setting priorities among the several new vaccines that are efficacious and have acceptable safety profiles.
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