Which type of immunity is characterized as being present at birth?

Natural immunity refers to the type of immune protection that an individual is born with, as opposed to immunity that is developed through exposure to pathogens or through medical interventions. At birth, an infant possesses a range of innate immune cells, including phagocytes and natural killer cells, which provide immediate defense against a variety of infections. Additionally, natural immunity includes barriers such as skin and mucous membranes, which serve as the first line of protection.

Unlike acquired immunity, which develops over time through exposure to specific antigens, natural immunity is non-specific and does not require previous exposure to a pathogen. Adaptive immunity involves a more specialized response that occurs after exposure to specific antigens, which is not present at birth. Passive immunity, on the other hand, refers to the temporary immunity gained through maternal antibodies transferred during pregnancy or through breastfeeding, but this is not inherent to the newborn itself.

Thus, natural immunity is the correct answer as it encompasses the innate defenses that are present from birth, providing immediate but non-specific protection against infections.