**Core Concept**
Active immunity is a type of immunity that is conferred on an individual by vaccination, which involves the production of antibodies against a specific pathogen. This immune response is mediated by the activation of T and B lymphocytes, resulting in long-term protection against future infections.

**Why the Correct Answer is Right**
When an individual receives a vaccine, the immune system recognizes the vaccine components as foreign and mounts an immune response. This response involves the activation of dendritic cells, which present antigens to T lymphocytes, leading to the proliferation of T and B lymphocytes. The B lymphocytes then produce antibodies specific to the pathogen, while the T lymphocytes provide cell-mediated immunity. This type of immunity is known as active immunity because it is initiated by the individual's immune system in response to the vaccine.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because it does not specify the type of immunity conferred by vaccination. There are several types of immunity, including active, passive, and cellular immunity.
**Option B:** This option is incorrect because it does not accurately describe the type of immunity conferred by vaccination. While vaccination can provide some level of protection, it is not the same as natural infection, which can lead to long-term immunity.
**Option C:** This option is incorrect because it is too broad and does not specifically refer to the type of immunity conferred by vaccination.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that vaccination provides long-term protection against specific pathogens, and booster shots may be necessary to maintain immunity over time.

**Correct Answer: A. Active immunity.