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Early trials of enterovirus 71 vaccine showed success
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Researchers with the Jiangsu Provincial Center for Disease Control and Prevention in China have reported that a new vaccine against enterovirus 71 is both immunogenic and well tolerated among healthy infants and children.
The researchers divided 360 children into two age groups: 1) aged 6 to 12 months and 2) aged 13 to 60 months. Both groups of children received either placebo or the EV-71 vaccine, which contained one of three dosages, either 160 U, 320 U or 640 U antigen per dose on day 1 or 1 month later.
The researchers reported that “after two doses, all the participants receiving EV-71 vaccines were seropositive and the seroconversion rates were greater than 98%. In the participants with seropositive baseline, one dose induced good seroconversion rates of greater than 64% in participants receiving EV-71.”
The researchers said although three serious adverse events occurred during the study, none were related to the vaccines. However, many of the participants, both controls and those who received the vaccine, reported injection site reactions.
The EV-71 vaccine could enter late stage clinical trials in about 5 years, with the help of biotech companies, according to published reports.
The researchers said although their findings may not be generalizable to all health care settings, “the results here warrant further study with the candidate EV71 vaccine in more diverse populations.”
Disclosure: Some of the researchers are employees of Beijing Vigoo Biological Corp.
Perspective
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José R. Romero, MD, FAAP
Enterovirus 71 (EV-A71), a member of the Picornaviridae, has been the cause of large outbreaks of hand, foot and mouth disease associated with significant neurologic disease and mortality, primarily in the Asia-Pacific region. The majority of severe neurologic disease and deaths occur in children aged younger than 5 years. Currently, no vaccine is available for prevention of EV-A71 infection.
Zhu and colleagues report the findings of a phase 1b trial using a formalin inactivated, alum adjuvanted EV-A71 vaccine in healthy Chinese infants and children aged younger than 5 years. Regardless of age and immunization dose, all subjects seronegative at baseline receiving two doses of vaccine, 28 days apart, achieved an arbitrarily predefined level of neutralizing antibodies. Seroconversion rates for this group exceeded 98%. For subjects seropositive at baseline (approximately one-third of all subjects), a single dose of vaccine induced seroconversion in greater than 64%.
The vaccine was well tolerated. The incidence of adverse events was not significantly different between vaccine recipients and the placebo group. However, a significant difference in the incidence of reactions was observed between those that received the highest dose vaccine formulation and placebo recipients. Fever and pain were the most common systemic and injection sitereactions, respectively. No severe adverse reactions were attributed to the vaccine.
Despite multiple limitations, this study documents for the first time that an inactivated EV-A71 vaccine can induce neutralizing antibodies and appears to be well tolerated in humans. It opens the way for continued development of a vaccine that may decrease the incidence of severe EV-A71 infection.
Limitations of the study included a small number subjects, high baseline seropositivity to EV-A71, lack of a clinically validated antibody level correlating with seroprotection, and lack of documentation that the vaccine could induce neutralizing antibodies against heterologous genotypes of EV-A71. Larger studies will be needed to document vaccine safety and efficacy. In particular, efficacy against heterologous genotypes of EV-A71. Future work will be needed to define the protective antibody level needed to prevent EV-A71 infection. Lastly, it will need to be shown that a vaccine against EV-71A does not interfere with the immunogenicity of routine childhood vaccines should it be administered concomitantly.
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