Close living quarter. It is strongly recommended that all college students living in dorms or frat houses (not just freshman) to get the Meningococcal vaccine due to it being highly contagious, relatively high mortality (death) rate, high morbidity (complication, amputation, etc.) rate, and ease of prevention (by getting vaccinated.) initial symptoms often mimic a common cold or flu so diagnosis can be delayed.
Proximity. Dorms, classes, cafeterias or military barracks, some infections are more likely to pass among populations in close proximity. The higher risk populations share similar settings. Meningococcal disease is also carried by some in their nasal passages without ever getting ill. Proximity, carriers and time duration of contact all add to the process.
Closeness. Age of starting college along with the close quarters of dormitories added to the point of being around all new strangers with their own illnesses/ viruses that a freshman may have never been exposed to before.
YES. Yes, but the peak risk actually starts rising around 13-14 yo and kids should be getting this shot at 11 yo now. Currently the CDC says to get one at 11 yo and another at 16 yo.
Absolutely. It is particularly devastating illness that is easily transmitted between persons in close proximity, and appears easier in teens/twenties. All should be vaccinated.