This will be a prospective observational study aiming to investigate immune health biomarkers and fecal microbiota in 48-60 Filipino breastfed infants from birth to 12 months of age. An optional follow-up period of approximately 2 years will follow.

This will be a prospective observational study in healthy term infants who are exclusively breastfed. Approximately 48-60 healthy breastfed infants aged ≥14 to ≤35 days at enrollment will be recruited and followed up until 12 month of age at 6 on-site visits: V1 (baseline), V3 (2 months), V5 (4 months), V6 (6 month), V7 (10months) and V8 (12 months).

The 12-month observational period will be followed by a 2year optional follow-up period for a total duration of the study of approximately 3 years.

The primary objective of this clinical study is to characterize early immune system development in breastfed Filipino infants by investigating infant blood markers of systemic immunity.

The secondary objectives will include the characterization of infant fecal markers of immune health and gut barrier function, infant blood and fecal microbiome, interactions between immune development and microbiome maturation, infant fecal metabolic profile and fecal pH, infant gastrointestinal (GI) tolerance, infant anthropometric measurements, infant complementary food intake as well as infant illness and infection.

Inclusion Criteria:

1. Written informed consent is obtained from parent(s)/ legally authorized representative(s) (LAR(s)).

2. Parent(s)/ LAR(s) must be able to provide evidence of parental authority and identity.

3. Parents/ LARs must understand the informed consent and other study documents.

4. Infants whose parent(s)/ LAR (s) has consented to blood collection as per protocol.

5. Able to temporarily store stool samples in a household freezer.

6. Infants whose parent(s)/LAR(s) are willing and able to comply with scheduled visits, and the requirements of the study protocol.

7. Infants whose parent(s)/LAR(s) can be contacted directly by telephone throughout the study.

8. Infants must meet all the following inclusion criteria to be eligible for enrollment into the study:

   1. Healthy term infant (≥37 weeks of gestation)
   2. At enrollment visit, postnatal age ≥14 to ≤35 days (date of birth = day 0)
   3. Birth weight is appropriate for gestational age (i.e., ≥ 2500g and ≤ 4500g)
   4. Infant has exclusively received breastmilk from birth to enrollment, and parent intends to continue exclusive breastmilk feeding until infant age 6 months.

Exclusion Criteria:

1. A medical condition or history that could increase the risk associated with study participation or interfere with the interpretation of study results, including:

   1. Evidence of major congenital malformations (e.g., cleft palate, extremity malformation).
   2. Suspected or documented systemic or congenital infections (e.g., human immunodeficiency virus, cytomegalovirus, syphilis).
   3. Previous or ongoing severe medical or laboratory abnormality (acute or chronic) which, in the judgment of the investigator, would make the infant inappropriate for entry into the study. Of note, children who are normally healthy but at the time of enrolment suffering from acute illness in a minor condition which are common in childhood and do not require some of the exclusionary medication mentioned below can be enrolled.

2. Presently receiving or have received prior to enrolment any of the following: medication(s) or supplement(s) which are known or suspected to affect the following: fat digestion, absorption, and/or metabolism (e.g., pancreatic enzymes); stool microbiota and characteristics (e.g., oral, or systemic antibiotics, glycerin suppositories, bismuth-containing medications, docusate, Maltsupex, or lactulose); growth (e.g., insulin or growth hormone); gastric acid secretion.

3. Infants whose parent(s) has(ve) not reached legal age of majority (18 years old) upon enrollment.

4. Currently participating or having participated in any interventional clinical trials since birth.

Approximately 60 healthy breastfed infants aged ≥14 to ≤35 days at enrollment. To ensure balanced sex representation of the study population, approximately 30 males and 30 females will be enrolled in the study.