Long-term protection of an inactivated enterovirus type 71 vaccine against hand, foot, and mouth diseases in children: a modelling study.

OBJECTIVES

Despite the availability of enterovirus type 71 (EV71) vaccines, evidence on long-term protection remains limited. We aimed to establish a mathematical model for predicting the 20-year long-term protection of the EV71 vaccine.

METHODS

We utilized data from a phase 3 trial in which infants and young children were randomized to receive either two doses of 400 U EV71 vaccine or placebo. Neutralizing antibody data (NTAb) were obtained from the immunogenicity subpopulation who were followed for 5 years. We compared candidate decay models using Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC), and selected the Segmented Power-law Model to fit antibody decay kinetics. Simulated datasets were generated via 10,000 iterations of Bootstrap sampling. We introduced dynamic exposure simulation with differential exposure rates before and after 2017, and applied a Scaled Logit Model to establish the association between NTAb titers and protective efficacy. Additionally, we performed stratified analysis by dividing the population into High, Medium, and Low responders based on initial antibody titers. Uncertainty was quantified using 95% confidence intervals (CI).

RESULTS

The predicted geometric mean titers (GMT) were 168.30 (95% CI: [139.76, 202.67]) at Month 1, 111.28 (95% CI: [93.15, 132.95]) at Month 6, 93.80 (95% CI: [79.12, 111.20]) at Month 12, and 68.04 (95% CI: [60.38, 76.68]) at Month 240. The model predicts that the EV71 vaccine provides a protective efficacy of 80.19% (95% CI: [78.69%, 81.70%]) at Month 1, declining to 72.57% (95% CI: [71.35%, 73.80%]) at Year 20. Stratified analysis revealed that High Responders maintained 75.58% protection at Year 20, compared to 65.09% for Medium and 64.99% for Low Responders.

CONCLUSION

Under the current EV71 epidemic conditions in China, the two-dose regimen of the inactivated EV71 vaccine provides durable protection exceeding 72% for at least 20 years.