ENTEROVIRUS 71 (EV71) is the causative agent of a variety of diseases ranging from hand, foot and mouth disease (HFMD) to severe neurological disorders, including meningitis, encephalitis and a polio-like paralysis that primarily affects young children. An EV71 infection is usually self-limiting and without residual disability, but in some cases there is significant central nervous system injury, multi-system disease and even death. In recent years, large-scale outbreaks of EV71 infections with many fatal cases have occurred in the Asia-Pacific region, particularly in China.
India and Indonesia are the two countries in the region that have not seen any outbreak of EV71 so far. But the two epidemics of HFMD that India has had so far—one in Kerala in 2003 and one in West Bengal in 2007—have given rise to concern even though no EV71 was isolated in either epidemic. Also, in 2003, scientists of the Enterovirus Research Centre, Mumbai, reported that EV71 was isolated from a five-year-old boy from Faridabad, Haryana, with acute flaccid paralysis.
The New England Journal of Medicine recently published the results of two randomised, placebo-controlled, double-blind, phase III trials of cell-culture-based inactivated EV71 vaccines against the subtype C4 that is the predominant genotype in China. The successful development of a vaccine in China is significant for India.
In a manufacturer-sponsored randomised trial conducted at 35 sites in Jiangsu Province, 10,077 healthy infants aged from six to 35 months received four weeks apart two intramuscular injections of either an alum-adjuvanted EV71 vaccine (developed by Sinovac Biotech, China) or a placebo. During a 12-month surveillance period, 0.3 per cent of vaccinees and 2.1 per cent of controls developed an EV71-associated disease. Vaccine efficacy was found to be 94.8 per cent against such disease and 100 per cent both in preventing EV71-associated hospitalisation and in preventing neurologic complications. Among participants who received two vaccine doses, 98.8 per cent developed protective titres of neutralising antibodies by day 56. In a randomised trial conducted in seven counties of the Guangxi Zhuang Autonomous Region, 12,000 healthy children aged from six to 71 months received with a four-week interval between doses two intramuscular injections of either a EV71 vaccine developed by the Institute of Medical Biology, Chinese Academy of Medical Sciences, or a placebo. In the subgroup tested for immunogenicity, 100 per cent of those who received the two doses showed seroconversion at day 56. Over the course of two epidemic seasons, vaccine efficacy against EV71-associated HFMD was 97.4 per cent. Last year, Lancet published the results of a randomised phase III trial involving 10,245 participants and a vaccine of another company (Beijing Vigoo Biological), which showed 90 per cent efficacy. Vaccines are also being developed in Singapore and Taiwan.
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