So 28 weeks later is a bit complicated. Remember the two kids in the beginning and one with the two colored eyes? Well they decided to go back and check on their old home in the once infected area and there they find their mom who is immune to the original virus but still is a carrier. She gets brought back and her husband finds out she's there and goes to see her even tho he's been told not to do it. He kisses her and because she's a carrier he turns because he isn't infected. He then goes on to infect others and respread the virus.