the infected is the first Pandora, the Lancelot girl (I must corrected my spoiler at page 18)...but then if the Pandora is a hybrid between human and Nova, what about Limiter? they "injected" by some Stigma fragment from their Onee-chan
do they have possibilities to become Nova's too?
about Aoi,
he's being protected not only because that...around 3 reason IMO
1.GENETICS (aka.Military) take interest in his Genuine Stigma Body, where he isn't officially received any Stigma Fragment from any donor
except....(read my spoiler at page 18)
2.Yumi Kim sensei feel sorry/sympathy to him...due to he is the last family member of the girl whom she adore in the past (Kazuha Aoi)
3.Bridgett L.Satellizer will run Amok if anything happened to Aoi. Even as junior, she considered as 'Monster' , she even managed to scared away a Battle-talented Pandora in the past (while Satellizer begin her debut as Touch Prohibited Queen and some upperclassmen sent to shut her down)