Evaluation of enterovirus A71 vaccine effectiveness against pediatric hand, foot, and mouth disease caused by enterovirus A71 virus in Tianjin, China, 2016-2023: A test-negative design case-control study.

Hand, foot and mouth disease (HFMD) caused by enterovirus A71 (EV-A71) is a common acute viral disease that mainly affects children under 5 years and often occurs in outbreaks or clusters in China. Given the high disease burden of HFMD and the absence of an effective drug for treating HFMD, the first inactivated monovalent EV-A71 vaccine was licensed in China in 2016. However, no study has assessed the long-term effectiveness of the EV-A71 vaccine on a large scale. A test-negative design case-control study was conducted to estimate the long-term vaccine effectiveness in Tianjin from 2016 to 2023. HFMD patients with a positive EV-A71 were assigned to the case group, and those with a negative EV-A71 were assigned to the control group. Logistic regression models were used to estimate the effectiveness of the vaccine. A total of 7,221 HFMD patients aged 6 months to 13 years old were included between 2016 and 2023. There were 510 (7.1%) children who tested positive for EV-A71, while 5,160 (71.5%) tested positive for other EVs, and 1551 (21.5%) tested negative for all EVs. Vaccine effectiveness was estimated to be 91.01% (95% CI: 84.03-95.53) for the study population. As for children aged 6-35 months, the vaccine effectiveness was 83.45% (95% CI: 68.28-92.58); while that was 96.97% (95% CI: 90.56-99.50) for children aged more than 35 months. The inactivated monovalent EV-A71 vaccine was found to be effective in preventing the HFMD caused by EV-A71 infection.