**Core Concept**
Rubella, also known as German measles, is a highly contagious viral infection affecting various age groups, but certain populations are prioritized for vaccination due to their vulnerability to serious complications. The primary goal of rubella vaccination is to prevent congenital rubella syndrome (CRS), which can lead to severe birth defects.

**Why the Correct Answer is Right**
The correct answer is **school-aged children**. The rubella vaccine is part of the measles, mumps, and rubella (MMR) vaccine, which is usually administered to children at 12-15 months of age and a booster dose at 4-6 years of age. This vaccination strategy aims to prevent the spread of rubella among school-aged children, thereby reducing the risk of CRS in pregnant women. The rubella vaccine induces immunity in most recipients, thereby decreasing the circulation of the virus in the community.

**Why Each Wrong Option is Incorrect**
* **Option A:** Infants under 6 months are not a priority for rubella vaccination due to the presence of maternal antibodies, which provide protection against the virus.
* **Option B:** Pregnant women are not a priority for rubella vaccination, but rather are advised to avoid exposure to the virus to prevent CRS.
* **Option C:** Adults over 40 years are not a priority for rubella vaccination, as they are no longer susceptible to CRS.

**Clinical Pearl / High-Yield Fact**
Rubella vaccination is a crucial public health measure to prevent CRS, which can lead to severe birth defects, including hearing loss, vision impairment, and heart defects.

**Correct Answer:** C. School-aged children.