As with all other organs and systems in the body, a newborn is not born with a fully developed immune system at birth. Rather, their immunity - a protective function consisting of cells, proteins, and organs - grows and strengthens with time, striving with each new day to keep them safe from the multitude of pathogens that they encounter in their environments.
At birth, a baby’s immune system is still quite weak and sensitive. Given its fragility, nature has compensated for this by endowing mothers with the ability to transfer their immunity onto their baby (called passive immunity) by way of antibodies through breast milk. A mother’s breast milk is filled with protective immunoglobulins that work to fight off bacteria and viruses that could be harmful to it. This supports the fact that breastfed babies get sicker much less than formula-fed babies.
