How long does passive immunity last?

Passive immunity lasts for a short time because it is acquired through the transfer of antibodies from one individual to another. This type of immunity is temporary, as the recipient does not produce their own antibodies. For example, a newborn receives antibodies from their mother through the placenta during pregnancy and through breast milk after birth. These antibodies provide immediate protection but gradually diminish as the infant's immune system grows and begins to produce its own antibodies. As a result, passive immunity typically does not last long enough to provide long-term protection against pathogens.

In contrast, active immunity, which occurs when an individual’s own immune system produces antibodies in response to an infection or vaccination, can last for many years or even a lifetime. Understanding the distinctions between passive and active immunity is important for recognizing how immunity functions in different contexts.