Given below are two statements. One is labeled as Assertion (A) and the other is labeled as Reason (R).
Assertion (A) : CDC recommends dengue vaccination (Dengvaxia) for 9 to 16 years old children but only when they have been previously infected with dengue and living in areas where dengue is common.
Reason (R) : Children without previous dengue infection are at increased risk for severe dengue disease and hospitalisation if they get dengue after they are vaccinated with Dengvaxia.
In light of the above statements, choose the correct answer from the option given below. 

Those who have not been previously infected with the dengue virus are at increased risk for severe dengue disease when vaccinated and subsequently infected with the virus due to a phenomenon known as antibody-dependent enhancement (ADE).
When a person is infected with dengue virus for the first time, their immune system produces antibodies specific to that particular strain of the virus. These antibodies help neutralise the virus. However, if the person is later infected with a different strain of the dengue virus, the antibodies produced during the first infection may not effectively neutralise the new strain. Instead, these antibodies might actually facilitate the entry of the virus into immune cells (like monocytes) through Fc receptors. This can lead to increased viral replication within these cells, causing more severe case of dengue disease than in people who had never been infected before.