I am legend movie help?

just a few questiond from i am legend movie... how does everyone get infected initially? and what does it mean when they ralk about something going airborne? and how did some poeple not get infected by this cancer cure when 99% of world died?

The woman who created the KV virus meant for it to be a cure for cancer, but apparently the side effects were much worse. Originally the virus was spread by contact, but it soon became a virus that could be spread by coughing, sneezing, and talking. If someone inhaled air with the virus in it, they became infected. That is what they meant when the said it went airborne. Not everyone got infected by it, one percent of the people were immune. But the almost all of the uninfected were eaten by the infected. When the disease goes airborne, it it much more contagious, so I'm guessing that somehow the infected got to other parts of the US even though they cut off all transportation in and out of New York. Or it might have infected animals such as birds, who flew to other parts of the world and infected people. It couldn't be controlled.

From the initial 10,000 or so trial patients for the cancer cure with the measles virus( I think that was the disease) trial. Starts as a contact transmission ( bite, scratch) and mutates to airborne virus. After it goes airborne it is unstoppable. Some people have a natural immunity to diseases in real life and it stands to reason that some would be immune to this one. Hope I answered your question well enough.