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The Centre for Health Protection (CHP) of the China Department of Health is investigating an outbreak of hand, foot and mouth disease (HFMD) at a residential child care center in Causeway Bay, Hong Kong.

Affected children tested positive for enterovirus (EV71) which usually causes HFMD. According to researchers Qiben Leng and Annie De Groot, the failure of polio vaccine efficacy or ‘take’ may contribute to these sporadic epidemics. They found a conserved immunodominant epitope between EV71 (HFMD) and poliovirus, using the JanusMatrix tool  (which looks at both the TCR facing residues). In other words, HFMD outbreaks could occur where polio vaccination has failed, due to lack of refrigeration or other breaks in the cold chain that (might) go unreported.

In 2012, Leng and De Groot discovered a cross-conserved epitope between EV71 and polio vaccine that is highly conserved among human enteroviruses. Specifically, cross-reactivity between the EV71 A3 epitope and the A3v epitope of poliovirus 3 Sabin strain induced protective, cross-reactive T cell responses. Assuming that this T cell epitope confers protection, it is possible that exposure to polio could protect against EV71 (HFMD). Since the type of polio vaccine distributed in China is still predominantly oral vaccine, vaccine efficacy might be adversely affected by breaks in the cold chain (such as leaving the vaccine outside, in a non-refrigerated system, while transferring the vaccine from one place to another). Whether or not patients were effectively immunized against Polio virus may determine the severity of their HFMD symptoms.

The hypothesis is simple to test – check polio antibodies. Antibodies to polio vaccine should be present in pre-vaccinated populations living in the same location as the HFMD patients, and absent when the patients are not vaccinated. At the very least, it is worth looking to see if the polio titers are uniformly positive in patients affected by HFMD!