Dragon follow-up aims to evaluate the growth, allergies, and infections of Chinese subjects up to four years of age who completed the intervention period visit (from Day 0-44 to Week 17) of the Dragon study [EBB16SI08406]. This study aims to provide insights into the role of usage of a partially hydrolyzed formula with added synbiotics in early life children's growth and immune-related outcome up to 4 years of age.

After providing informed consent, subjects from the prior randomized controlled trial (Dragon study) will be enrolled in the follow-up study. The observation period is from the end of the Dragon study (12 months) to 4 years of age. Data from the end of the Dragon study to the actual age at the enrolment (with 4 years of age as the upper limit) will be collected retrospectively, and data from the actual age at the enrolment (if younger than 4 years of age) to 4 years of age will be collected prospectively. Data will be collected retrospectively or prospectively at four scheduled visit timepoints: 24 months, 30 months, 3 years and 4 years of age. The visit points are in accordance with the health assessment schedule of the Maternal and Children Health Network in China to ensure the data on growth before the start of this follow-up study is available.

As required by relevant law issued by the National Health and Family Planning Commission in China, the maternal and children health network institutions in all provinces should carry out regular health assessments for children aged 0-6 years, in which the growth evaluations should be conducted for children aged 24 months, 30 months, 3 years and 4 years. In this follow-up study, the weight and height parameters will be obtained from the Children's Health Manual, and skinfolds thickness at 4 years of age will be measured on-site by trained personnel.

Except for stool microbiota collection and skinfold thickness measurement, all variables will be collected via our online tools. Data on growth parameters, allergy, infection, medications, and hospitalization will be collected using an electronic data capture system (EDC). Parents are expected to login to an electronic platform at a scheduled time from an Internet-accessible smartphone or tablet to fill the online questionnaire and send photocopies of examination results as required (any information related to personal privacy such as name, address and hospitalization ID should be covered before being taken a photocopy, see section 11.5). Parents will receive reminder short messages on the first day of the scheduled visit window. Those who fail to respond to the follow-up message in two weeks will receive a backup telephone call to complete the filling.

The gastrointestinal symptoms, stool assessment, skinfold thickness and dietary pattern and behaviour will only be collected prospectively. If the subjects' actual age at the enrolment is older than 4 year old, skinfolds thickness, gastrointestinal symptoms, stool assessment and dietary pattern and behaviour at 4 years of age will not be collected.

Inclusion Criteria:

• Children completed the intervention period visits (from Day 0-44 to Week 17) of the Dragon study in one of the randomized groups or in the breastfeeding reference group.
• Children whose parents provide informed consent for participation in the Dragon Follow Up study.

Exclusion Criteria:

• Participated or currently in another interventional clinical trial.

The study population consists of healthy term-born children who completed the intervention period visit (from Day 0-44 to Week 17) of the preceding Dragon study, irrespective of whether they participated in one of the randomised groups or in the breastfeeding reference group. In total, 226 subjects had completed the Week 17 visit in the Dragon study. The subjects will be enrolled in the Dragon follow up after obtaining informed consent from their parents for the follow-up study.