Safety and Immunogenicity of a ChAd155-Vectored Respiratory Syncytial Virus (RSV) Vaccine in Healthy RSV-Seropositive Children 12-23 Months of Age.

BACKGROUND: Safe and effective respiratory syncytial virus (RSV) vaccines remain elusive. This was a phase I/II trial (NCT02927873) of ChAd155-RSV, an investigational chimpanzee adenovirus-RSV vaccine expressing 3 proteins (fusion, nucleoprotein, and M2-1), administered to 12-23-month-old RSV-seropositive children followed up for 2 years after vaccination. METHODS: Children were randomized to receive 2 doses of ChAd155-RSV or placebo (at a 1:1 ratio) (days 1 and 31). Doses escalated from 0.5 × 1010 (low dose [LD]) to 1.5 × 1010 (medium dose [MD]) to 5 × 1010 (high dose [HD]) viral particles after safety assessment. Study end points included anti-RSV-A neutralizing antibody (Nab) titers through year 1 and safety through year 2. RESULTS: Eighty-two participants were vaccinated, including 11, 14, and 18 in the RSV-LD, RSV-MD, and RSV-HD groups, respectively, and 39 in the placebo groups. Solicited adverse events were similar across groups, except for fever (more frequent with RSV-HD). Most fevers were mild (≤38.5°C). No vaccine-related serious adverse events or RSV-related hospitalizations were reported. There was a dose-dependent increase in RSV-A Nab titers in all groups after dose 1, without further increase after dose 2. RSV-A Nab titers remained higher than prevaccination levels at year 1. CONCLUSIONS: Three ChAd155-RSV dosages were found to be well tolerated. A dose-dependent immune response was observed after dose 1, with no observed booster effect after dose 2. Further investigation of ChAd155-RSV in RSV-seronegative children is warranted. CLINICAL TRIALS REGISTRATION: NCT02927873.

Respiratory syncytial virus (RSV) is among the main causes of bronchiolitis and pneumonia regularly leading to hospitalization in children. A safe and effective vaccine to prevent RSV infection in this age group has not yet been found, despite great efforts over several decades. This study tested a new candidate RSV vaccine, expressing 3 important pieces of the virus, in toddlers who already had a previous RSV infection. The vaccine was generally well tolerated. Vaccination triggered antibodies against RSV that were able to block the virus in laboratory tests and that persisted for 1 year.

Efficacy, safety, and immunogenicity of an inactivated, adjuvanted enterovirus 71 vaccine in infants and children: a multiregion, double-blind, randomised, placebo-controlled, phase 3 trial.

BACKGROUND: Children are susceptible to severe or fatal enterovirus 71 (EV71) infections. We aimed to evaluate the efficacy, safety, and immunogenicity of EV71vac, an aluminium phosphate-adjuvanted inactivated EV71 vaccine in children aged 2-71 months. METHODS: We did a randomised, double-blinded, placebo-controlled, phase 3 trial at five hospitals in Taiwan and two in Vietnam. Children aged 2-71 months were stratified by country and age, and randomly assigned (1:1) to receive two doses of EV71vac or placebo via intramuscular injection 56 days apart. Children aged 2-23 months received a third booster dose on day 366. The primary endpoint was the clinical efficacy of the total vaccinated cohort against EV71-associated diseases during the follow-up period, from 14 days after the second dose to when 15 cases of EV71 infections were confirmed in the per-protocol population. Our safety analysis included all participants who received at least one dose of EV71vac. This trial is registered with ClinicalTrials.gov, NCT03865238, and is complete. FINDINGS: Between April 23 and Dec 25, 2019, of 3663 children assessed, 3061 were randomly assigned, of whom 3049 were vaccinated: 1521 children in the EV71vac group and 1528 in the placebo group. By May 20, 2021, our primary efficacy analysis included 2959 children, with 1476 children in the EV71vac group and 1483 children in the placebo group. The vaccine efficacy of EV71vac was 96·8% (95% CI 85·5-100) against EV71 associated diseases (p<0·0001). The percentage of participants who reported solicited adverse events were similar in both groups: 865 (56·9%) in the EV71vac group and 852 (55·8%) in the placebo group. Almost all reported solicited adverse events were mild and self-limited. INTERPRETATION: EV71vac is safe, well-tolerated, and highly effective in preventing EV71 associated diseases in children aged 2-71 months. FUNDING: Medigen Vaccine Biologics and A+ Industrial Innovative R&D Program of the Ministry of Economic Affairs, Taiwan.

Inoculation Age of Bacillus Calmette-Guérin Tokyo-172 Strain and Vaccine-related Adverse Reactions in Taiwan Birth Cohort of 2012-2017.

BACKGROUND: In 2016 in Taiwan, inoculation with the Bacillus Calmette-Guérin (BCG) Tokyo-172 vaccine was postponed from 24 hours after birth to 5-8 months of age. We reviewed BCG-induced adverse reactions reported to the Vaccine Injury Compensation Program (VICP) to identify differences between early and delayed BCG inoculation. METHODS: Clinical presentations of BCG-related adverse reactions reported to VICP for the 2012-2017 birth cohort were reviewed until the end of 2019. The correlations between inoculation age and complications were evaluated. RESULTS: We analyzed 233 BCG adverse reactions, including regional lymphadenitis (33.9%), injection site reactions (35.2%), osteitis/osteomyelitis (27.9%), and distant soft tissue infections (3.0%). The incidence of osteitis/osteomyelitis was lower when vaccination was done after 5 months of age (relative risk [RR], 0.32; 95% confidence interval [CI], .16-.64). Injection site reactions (RR, 8.82; 95% CI, 5.04-15.44) and lymphadenitis (RR, 2.24; 95% CI, 1.44-3.45) were significantly more common in vaccinees older than 5 months. Shorter onset durations of mild adverse reactions (lymphadenitis and injection site reactions) were reported in vaccinees older than 5 months, while no statistical significance was found regarding osteitis/osteomyelitis. CONCLUSIONS: Osteomyelitis and distant soft tissue infection may occur less frequently when BCG inoculation occurs after 5 months of age, although mild adverse reactions can be more frequent, symptom onset times can be shortened. As few severe reactions might occur more than 2 years after BCG inoculation and the policy of delayed BCG inoculation was implemented in 2016, a longer observational period is needed to clarify the exact severe complications decrement.

Immunogenicity and safety of porcine circovirus-free human rotavirus vaccine in healthy infants: a phase III, randomized trial.

BACKGROUND: Porcine circovirus type 1 (PCV-1) material was detected in the human rotavirus vaccine (HRV) in 2010. In this study (NCT02914184) we compared immunogenicity and safety of the PCV-free HRV vaccine (PCV-free HRV) with HRV. PCV-free HRV is an HRV with no detection of PCV-1 and PCV-2 according to the limit of detection of the tests used. METHODS: Healthy infants 6-12 weeks of age were randomized (1:1:1:1) to receive 2 doses of 1 of the 3 lots of PCV-free HRV or HRV. The study objectives were to demonstrate lot-to-lot consistency of the PCV-free HRV and non-inferiority of PCV-free HRV as compared to HRV in terms of immunogenicity, 1-2 months post-dose 2. Reactogenicity and safety were also assessed. RESULTS: Overall, 1612 infants were enrolled and 1545 completed the study. Study objectives were demonstrated since the pre-defined criteria were met. Among participants receiving PCV-free HRV and HRV, 79.27% and 81.76% seroconverted and geometric mean concentrations were 159.5 and 152.8 U/mL, respectively. The incidences of adverse events and serious adverse events were similar between the pooled PCV-free HRV and HRV groups. CONCLUSIONS: The 3 PCV-free HRV lots demonstrated consistency and PCV-free HRV was non-inferior compared to HRV in terms of immunogenicity.

Cost-effectiveness evaluation of the 10-valent pneumococcal non-typeable Haemophilus influenzae protein D conjugate vaccine for children in Taiwan.

BACKGROUND: Streptococcus pneumoniae (S. pneumoniae) and non-typeable Haemophilus influenzae (NTHi) are substantial contributors to morbidity and mortality of diseases including invasive pneumococcal diseases (IPDs), pneumonia and acute otitis media (AOM) worldwide. In Taiwan, 10-valent pneumococcal polysaccharide and NTHi protein D conjugate vaccine (PHiD-CV) and 13-valent pneumococcal conjugate vaccine (PCV13) are licensed in children against pneumococcal disease. In addition to S. pneumoniae, clinical trials suggest efficacy of PHiD-CV against NTHi AOM. This study aims at evaluating the cost-effectiveness of a 2 + 1 schedule of PHiD-CV vs. PCV13 2 + 1 in the universal mass vaccination program of infants in Taiwan. METHODS: A published Markov cohort model was adapted to simulate the epidemiological burden of IPD, pneumonia and AOM for a birth cohort in Taiwan over 10 years. The probability of entering a specific health state was based on the incidence rate of the diseases. Only direct medical costs were included, and costs and outcomes were discounted annually. Vaccine efficacy assumptions were based on published data and validated by a panel of independent experts. Clinical, epidemiological, and serotype distribution data were based on locally published data or the National Health Insurance Research Database. Price parity of vaccines was assumed. Published pneumococcal disease-related disutility weights were used due to lack of local data. Incremental cost-effectiveness ratio was calculated and benchmarked against the recommended threshold in Taiwan. Extensive one-way sensitivity analysis, alternative scenarios and probabilistic sensitivity analysis were performed to test the robustness of the results. RESULTS: PHiD-CV would potentially reduce the number of NTHi-related AOM cases substantially and prevent comparable IPD and pneumonia-related cases and deaths compared to PCV13. Over a 10-year horizon, PHiD-CV is estimated to dominate PCV13, saving 6.7 million New Taiwan Dollars (NTD) and saving 21 quality-adjusted life years. The result was robust over a wide range of sensitivity analyses. The dominance of PHiD-CV was demonstrated in 90.5% of the simulations. CONCLUSIONS: PHiD-CV 2 + 1 would provide comparable prevention of IPD, pneumonia cases and additional reduction of NTHi-AOM cases, and is considered dominant compared with PCV13 2 + 1 in Taiwan.

Impact of Wearing Masks, Hand Hygiene, and Social Distancing on Influenza, Enterovirus, and All-Cause Pneumonia During the Coronavirus Pandemic: Retrospective National Epidemiological Surveillance Study.

BACKGROUND: The coronavirus disease (COVID-19) pandemic is an important health crisis worldwide. Several strategies were implemented to combat COVID-19, including wearing masks, hand hygiene, and social distancing. The impact of these strategies on COVID-19 and other viral infections remains largely unclear. OBJECTIVE: We aim to investigate the impact of implemented infectious control strategies on the incidences of influenza, enterovirus infection, and all-cause pneumonia during the COVID-19 pandemic. METHODS: We utilized the electronic database of the Taiwan National Infectious Disease Statistics System and extracted incidences of COVID-19, influenza virus, enterovirus, and all-cause pneumonia. We compared the incidences of these diseases from week 45 of 2016 to week 21 of 2020 and performed linear regression analyses. RESULTS: The first case of COVID-19 in Taiwan was reported in late January 2020 (week 4). Infectious control strategies have been promoted since late January. The influenza virus usually peaks in winter and decreases around week 14. However, a significant decrease in influenza was observed after week 6 of 2020. Regression analyses produced the following results: 2017, R2=0.037; 2018, R2=0.021; 2019, R2=0.046; and 2020, R2=0.599. A dramatic decrease in all-cause pneumonia was also reported (R2 values for 2017-2020 were 0.435, 0.098, 0.352, and 0.82, respectively). Enterovirus had increased by week 18 in 2017-2019, but this was not observed in 2020. CONCLUSIONS: Using this national epidemiological database, we found a significant decrease in cases of influenza, enterovirus, and all-cause pneumonia during the COVID-19 pandemic. Wearing masks, hand hygiene, and social distancing may contribute not only to the prevention of COVID-19 but also to the decline of other respiratory infectious diseases. Further studies are warranted to elucidate the causal relationship.

Prevalence of preschool children developmental disabilities in northeastern Taiwan - Screening with Taipei City Developmental Screening Checklist for Preschoolers, 2nd Version.

BACKGROUND/PURPOSE: The prevalence of developmental disabilities in Taiwan remains unclear, especially in young children under the age 3. We aimed to study the prevalence of developmental disabilities and verify a useful developmental screening tool in a community setting in Taiwan. METHODS: We conducted a prospective cross-sectional study in northeastern Taiwan from July 2008 to December 2009 in children aged 4 months to 6 years old from well-child visits. We devised a screening program using Taipei City Developmental Screening Checklist for Preschoolers, 2nd Version (Taipei-II), a validated parent-report milestone checklist tailored to the Taiwanese culture and language to assess the prevalence of developmental disabilities in Taiwan. Information about the children's medical conditions and their family were recorded. RESULTS: A total of 3214 children were recruited, of whom 365 had developmental disabilities, with an overall prevalence of 11.36%. Speech and language delay/disorders were the most common developmental problems followed by motor delays, with prevalence rates of 4.79% and 2.33%, respectively. Low economic status, prematurity and/or small for gestational age and a history of perinatal hypoxia or underlying medical disorders were the main risk factors correlated with developmental delays. However, foreign-born mother and aboriginal families were not important factors for poor developmental outcomes. CONCLUSION: The prevalence rate of developmental disabilities in northeastern Taiwan was 11.36%. Low economic status, prematurity and/or small for gestational age and a history of underlying medical disorders were the main risk factors correlated with developmental disabilities. Taipei II is an easy-to-use and effective developmental surveillance tool for Taiwanese children.

Clinical Manifestations, Management, and Outcomes of Osteitis/Osteomyelitis Caused by Mycobacterium bovis Bacillus Calmette-Guérin in Children: Comparison by Site(s) of Affected Bones.

OBJECTIVE: To evaluate the clinical manifestations, management, and outcomes of Mycobacterium bovis Bacillus Calmette-Guérin (BCG) osteitis/osteomyelitis. STUDY DESIGN: We reviewed 71 cases of BCG osteitis/osteomyelitis registered in Taiwan's vaccine injury compensation program (VICP) in 1998-2014. Demographic, clinical, laboratory, treatment, and outcome data were compared according to site(s) of infection. RESULTS: Involvement of a long bone of the lower extremity was present in 36.6% of the children, followed by foot bone (23.9%), rib or sternum (15.5%), upper extremity long bone (9.9%), hand bone (7%), multiple bones (4.2%), and vertebrae (2.8%). Children with lower extremity long bone involvement had a longer interval from receipt of BCG vaccine to presentation (median, 16.0 months; P = .02), and those with foot bone infection had higher rates of swelling (94.1%; P = .02) and local tenderness (76.5%; P = .004). Surgical intervention was performed in 70 children, with no significant difference in the number of procedures by site (median, 1.0 procedure per patient). Among the 70 children who received antimicrobial therapy, those with vertebral and multifocal infections had a longer duration of treatment (P < .001) and/or second-line antituberculosis medications (P = .002). Three children with vertebral and multifocal infections had major sequelae with kyphosis or leg length discrepancy. Outcomes were good for children with involvement of the ribs, sternum, and peripheral bones without multifocal involvement. The average time for functional recovery was 6.2 ± 3.9 months. CONCLUSION: Children with BCG osteitis/osteomyelitis in different bones had distinct presentations and outcomes. Pediatricians should consider BCG bone infection in young vaccinated children with insidious onset of signs and symptoms, and consider affected site(s) in the management plan.

Application of Sonography in the Diagnosis and Follow-Up of Trapped Temporal Horn of Lateral Ventricle: Two Case Reports.

Trapped temporal horn of lateral ventricle (TTHLV) is a rare condition of isolated focal hydrocephalus. We report two cases with different presentations, etiologies, and surgical managements. The first case involved an extremely preterm male baby with a history of ventriculitis and intraventricular hemorrhage; he received external ventricle drainage twice due to obstructive hydrocephalus. TTHLV was detected by sonography. He received a ventriculoperitoneal shunt involving two catheters to bypass the adhesion site. There was no ventricular dilatation during 2 years of follow-up. The second case involved a term baby with an enlarged head; brain sonography revealed left focal hydrocephalus with TTHLV and mild midline shift. Neuroendoscopic cystoventriculostomy with fenestration from the left trigone to the frontal horn was performed and serial follow-up brain sonography for 3 months showed decreased ventricle size. The suitable surgical techniques for the management of TTHLV should be adjusted according to the patients' condition to obtain more favorable outcomes. Brain sonography can be a useful tool for the diagnosis and for following up the surgical outcomes in infants with TTHLV.

Normal Development of the Corpus Callosum and Evolution of Corpus Callosum Sexual Dimorphism in Infancy.

OBJECTIVES: The aim of this study was to establish reference ranges for the corpus callosum in infancy and to clarify how sexual dimorphism evolves between the fetal stage and infancy. METHODS: Normal sonograms from cerebral ultrasonographic examinations of 1- to 6-month-old healthy full-term infants were selected. The length and thickness of the corpus callosum were determined, and the effect of sex on these values was analyzed. Studies on corpus callosum sexual dimorphism were reviewed. RESULTS: In total, sonograms from 236 1- to 6-month-old infants (120 male and 116 female) were collected, and the typical values (5th-95th percentiles) of the corpus callosum were determined for each group. During the first 2 months, with and without brain size adjustment, the corpus callosum in female infants was significantly thicker than that in male infants (mean thickness ± SD: 1 month, male infant, 1.8 ± 0.3 mm; female infant, 2.1 ± 0.3 mm; P = .005; 2 months, male infant, 1.8 ± 0.2 mm; female infant, 2.0 ± 0.3 mm; P = .002). The corpus callosum thickness of male and female infants had no significant differences after 2 months of age. Sexual dimorphism was not detected in corpus callosum length. CONCLUSIONS: Our study provides reference data on typical corpus callosum development in infants. In the fetal period and early infancy, the corpus callosum in female infants is thicker than that in male infants. From 3 months onward, the corpus callosum sexual dimorphism becomes insignificant throughout childhood. The evolvement of corpus callosum sexual dimorphism suggests that maternal factors may influence brain development.

Posterior Fossa Hemorrhage in a Term Neonate with Hemophilia A.

Posterior fossa hemorrhage is rare in term baby and difficult to assess. The clinical signs are nonspecific and usually delay the diagnosis. We present a 5-day-old male neonate of posterior fossa hemorrhage with the initial presentations of fever and seizure and early deduced by cranial ultrasonography findings as hyperechoic, asymmetric, ill-defined density and complicated with hydrocephalus. Magnetic resonance imaging of the head verified the diagnosis. Hemophilia A was confirmed thereafter by serology.

Rare Brain Tumor in a Neonate.

Neonatal brain tumor is rare and its outcome is generally poor. We reported a 17-day-old neonate presented as enlarged head girth. The pathological finding showed an embryonal tumor with multilayered rosettes.

The Reversible Corpus Callosum Splenium Lesion in A Neonate with Hypoglycemia and Seizure.

PURPOSE: Reversible splenial lesion syndrome is a distinct clinicoradiological syndrome with diverse etiologies. Hypoglycemia induced reversible splenial lesion syndrome has been documented in adults and children, but rare in neonates. We demonstrate a neonate with hypoglycemia presenting with a typical reversible splenial syndrome. CASE REPORT: Patient A four-day-old male neonate had hypoglycemia and seizure, whose symptoms improved soon after glucose supplementation. Magnetic resonance imaging examination showed restricted diffusion of the splenium of the corpus callosum. Proton MR spectroscopy revealed a decreased N-acetylaspartate peak. The lesion resolved in subsequent MRI images. The patient is free from clinical symptoms and has normal development currently. CONCLUSION: The patient presented typical clinical course and radiological features of reversible splenial lesion syndrome. Through timely and proper treatment, the outcome could be favorable.

Preliminary Report of Nationwide COVID-19 Vaccine Compensation in Taiwan.

The potential adverse effects of coronavirus disease 2019 (COVID-19) vaccinations raise public concerns. Data from Taiwan's Vaccine Injury Compensation Program (VICP) can provide valuable insights. This study analyzed the preliminary application data for COVID-19 vaccine compensation in Taiwan's VICP, focusing on applicants receiving vaccines between March 2021 and June 2022. Among the 2941 adverse events, 113 cases (3.8%) were deemed causally associated with vaccination, 313 (10.6%) were indeterminate, and 2515 (85.5%) had no causal association. Nearly half (47.6%) of the applicants were over 60 years old, and 76.6% had a history of pre-existing chronic diseases. Among the 426 vaccine-associated or indeterminate cases, the most common causes were hematological diseases and thrombosis. There were 920 mortality cases reported, and 97.4% were unassociated with vaccination. Only five deaths were judged to be associated with the COVID-19 vaccination, all involving the adenovirus vector vaccine and thrombosis with thrombocytopenia syndrome. In conclusion, most compensation applications were not causally linked to vaccination. Compared to other countries, the number of applications in Taiwan's VICP is relatively high. These findings may indicate a need to adjust the application requirements for compensation in Taiwan's program.

Psychiatric disorders in term-born children with marginally low birth weight: a population-based study.

BACKGROUND: Marginally low birth weight (MLBW) is defined as a birth weight of 2000 ~ 2499 g. Inconsistent findings have been reported on whether children with low birth weight had higher rates of neurological, attention, or cognitive symptoms. No studies have explored the occurrence of clinically diagnosed psychiatric disorders in term- born MLBW infants. We aimed to investigate the risk of subsequent psychiatric disorders in term-born children with MLBW. METHODS: This is a nationwide retrospective cohort study, by analysing the data from Taiwan's National Health Insurance Research Database from 2008 to 2018. The study population includes propensity-score-matched term-born infants with MLBW and those without MLBW (birth weight ≥ 2500 g). Cox proportional hazard analysis was used after adjustment for potential demographic and perinatal comorbidity confounders. Incidence rates and hazard ratios (HR) of 11 psychiatric clinical diagnoses were evaluated. RESULTS: A total of 53,276 term-born MLBW infants and 1,323,930 term-born infants without MLBW were included in the study. After propensity score matching for demographic variables and perinatal comorbidities, we determined that the term-born MLBW infants (n = 50,060) were more likely to have attention deficit and hyperactivity disorder (HR = 1.26, 95% confidence interval (CI) [1.20, 1.33]), autism spectrum disorder (HR = 1.26, 95% CI [1.14, 1.40]), conduct disorder (HR = 1.25, 95% CI [1.03, 1.51]), emotional disturbance (HR: = 1.13, 95% CI [1.02, 1.26]), or specific developmental delays (HR = 1.38, 95% CI [1.33, 1.43]) than term-born infants without MLBW (n = 50,060). CONCLUSION: MLBW was significantly associated with the risk of subsequent psychiatric disorder development among term-born infants. The study findings demonstrate that further attention to mental health and neurodevelopment issues may be necessary in term-born children with MLBW. However, possibilities of misclassification in exposures or outcomes, and risks of residual and unmeasured confounding should be concerned when interpreting our data.

The clinical impact of primary granulocyte-colony stimulating factor prophylaxis in children with acute lymphoblastic leukemia who underwent induction chemotherapy.

BACKGROUND: Data describing the risk factors for the occurrence of severe infections in acute lymphoblastic leukemia (ALL) patients following induction chemotherapy and the role of prophylactic granulocyte-colony stimulating factor (G-CSF) in the era of antimicrobials prophylaxis are limited. METHODS: This study enrolled 188 children aged ≤18 years with newly diagnosed ALL who received Taiwan Pediatric Oncology Group ALL-2002 and 2013 treatments between January 1, 2010 and June 30, 2021. Prophylactic G-CSF was administered when a patient continues neutropenia after achieving the first bone marrow remission since June 1, 2015. Clinical factors were assessed for their association with severe infections. RESULTS: From January 2010 to May 2015, 80 children experienced a total of 11 (13.5%) episodes of severe infections; while 10 (9.2%) episodes were reported to occur in 108 patients who received prophylactic G-CSF. Reduction of severe infections occurrence did not achieve statistical significance during prophylactic G-CSF administration in ALL patients. Compared with ALL-high risk (HR) and very high risk patients with no G-CSF prophylaxis, the use of G-CSF prophylaxis significantly reduced episodes of febrile neutropenia. Occurrence of grade III-IV intestinal ileus, grade II-III oral mucositis, prolonged neutropenia, central venous catheter (CVC) placement, or the requirement insulin therapy for hyperglycemia were associated with higher risk of bloodstream infections. CONCLUSIONS: ALL-HR patients with G-CSF prophylaxis were associated with reduction of febrile neutropenia episodes. Occurrence of severe ileus, oral mucositis, hyperglycemia, CVC placement, or prolonged neutropenia were associated with severe infections in ALL patients receiving induction chemotherapy.

Long-Term Immunogenicity Study of an Aluminum Phosphate-Adjuvanted Inactivated Enterovirus A71 Vaccine in Children: An Extension to a Phase 2 Study.

Enterovirus A71 (EV-A71) causes hand, foot, and mouth disease in infants and children with potential for fatal complications such as encephalitis and acute flaccid myelitis. This study examined the long-term immunity conferred by EV71vac, an inactivated EV-A71 vaccine adjuvanted with aluminum phosphate, in children from the age of 2 months to <6 years, for up to 5 years after the first immunization. A total of 227 participants between 2 months and <6 years of age who had previously received either EV71vac or placebo in the phase two clinical study were enrolled. Subjects were divided into age groups: 2 years to <6 years (Group 2b), 6 months to <2 years (Group 2c), and 2 months to <6 months (Group 2d). At Year 5, the neutralizing antibody titers against the B4 subgenotype remained high at 621.38 to 978.20, 841.40 to 1159.93, and 477.71 to 745.07 for Groups 2b, 2c, and 2d, respectively. Cross-neutralizing titers at Year 5 remained high against B5 and C4a subgenotypes, respectively. No long-term safety issues were reported. Our study provides novel insights into the long-term immunity conferred by EV71vac in children aged from two months to six years, particularly in those who received EV71vac between two and six months of age.