Your friend tests her snake-wrangling skills on an eastern diamondback rattlesnake, and is bitten and envenomated (injected with the snake's venom). In the emergency department, doctors administer the antivenin CroFab, which contains antibodies to the toxins in snake venom. Is this an example of active or passive immunity? Will this confer any lasting protection to your friend?

Active immunity occurs when an individual's immune system is stimulated to produce antibodies in response to an antigen, such as a pathogen or toxin. This can happen naturally through infection or artificially through vaccination. The protection provided by active immunity is usually long-lasting, as the immune system retains memory cells that can respond quickly to future exposures.

Passive immunity involves the transfer of antibodies from one individual to another, providing immediate but temporary protection. This can occur naturally, such as when a mother passes antibodies to her baby through breast milk, or artificially through treatments like antivenin. Since the recipient's immune system does not produce its own antibodies, the protection typically lasts only a few weeks to months.

Antivenin, or antivenom, is a medical treatment that contains antibodies specifically designed to neutralize venom from snake bites or other venomous creatures. In the case of CroFab, it is derived from the plasma of immunized animals and is used to treat envenomation. While it provides immediate protection against the effects of venom, it does not confer lasting immunity, as the recipient's immune system does not develop memory against the venom.