A situation in which a person's immunity to one agent provides immunity to a related agent as well is called?

DSSSB - 29 August 2019 (Shift-2)

Microbiology

Easy

Appeared in: DSSSB - 29 August 2019 (Shift-2)

Explanation

Cross-immunity is the correct term for the phenomenon where immunity developed against one specific agent confers protection against a different but related agent.
This occurs because the two agents share similar surface structures, or antigens, which the immune system recognizes.
The classic example is the observation by Edward Jenner that milkmaids who contracted cowpox (a mild disease) were subsequently immune to smallpox, a much more severe and related virus.
This principle is fundamental to the development of some vaccines, where a less harmful but related organism is used to induce immunity.

Option A: Passive immunity involves the transfer of pre-made antibodies to an individual, providing immediate but temporary protection. It does not involve the individual's immune system creating a response to a related agent.
Option B: Herd immunity is a population-level concept, not an individual one. It describes how a high rate of immunity in a community can protect the few who are not immune by reducing the overall circulation of a pathogen.
Option D: Active immunity is a broad category referring to any immunity produced by an individual's own immune system. While cross-immunity is a type of active immunity, the term 'Cross-immunity' is the more specific and precise answer for the situation described.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Types of Immunity as background academic context rather than a clinical decision trigger.
Understanding cross-immunity is crucial in public health and vaccine development. For example, scientists study cross-reactivity between different strains of influenza virus to develop more effective seasonal flu vaccines.
It also helps explain why exposure to certain common cold coronaviruses might offer a degree of protection against more severe coronaviruses like SARS-CoV-2.
What if? If two viruses are antigenically very different (e.g., measles and influenza), there would be no cross-immunity. An individual immune to measles would still be fully susceptible to influenza, highlighting the specificity of the immune response.

How to Approach the Question

First, carefully read the question and identify the key phrase: 'immunity to one agent provides immunity to a related agent'.
Analyze the keywords. 'Related agent' is the most critical clue. This implies a connection or similarity between two different pathogens.
Evaluate each option based on this key phrase.
Eliminate 'Passive immunity' as it involves receiving antibodies, not generating a response.
Eliminate 'Herd immunity' as it's a community-level concept, not individual protection against a related agent.
Differentiate between 'Active immunity' and 'Cross-immunity'. Recognize that 'Active immunity' is a broad category, while 'Cross-immunity' is the specific term for the exact scenario described in the question.

Concept Tested & Keywords

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