englischen text korrigieren

Du tust also so, als wäre es 2012 und erzählst das, was "jetzt" passiert, richtig? AH! Nein, ich sehe den Namen einer Schauspielerin - es ist also eine Zusammenfassung eines Film?

Here we go:

New York, 2012: Humanity beats cancer.

In any case, some scientists believe(d) this.
An artificially made virus, named after its inventor Dr. Alice Kripper (Emma Thompson), is supposed to destroy [straight?] cancer cells. However, the virus has unexpected and exceedingly fatal side effects; 90% of the population die; 0.2% are immune; all remaining people fall ill and show symptoms similar to rabies and [unbelievable] aggressive behaviour against the non- infected. The virus spreads in organisms and, within a short time, exterminates almost the entire population.
Frage: das hast du doch eben schon gehabt: 90% der Bevölkerung sterben....?

A handful of survivors, maybe the only one that has not been infected with the virus is ambulance- man Dr. Robert Neville ( Will Smith who plays the male main character).
Frage: du sprachst doch vorher von 0,2% der Bevölkerung - hier jetzt "der einzige"?

He lives in the once pulsating, now extint metropolis New York, together with his sheepdog as his only companion. His wife Zoe ( Salli Richardson) and his little daughter Marley ( Willow Smith) have are in a helicopter collision during the chaotic evacuation of the city in 2009.
Dr. Neville, however, is not alone in New York: a dangerous horde of infected people track him. The virus has left a small group of survivors, who are now mentally deranged and show extremely aggressive behaviour which makes it hard to still call them human beings. They react sensitively to ultraviolet light and mainly creep out of the city´s ruins at night. Still, Dr. Neville has hope: if he is immune to the epedemic, maybe there are other survivors elsewhere on the planet. It might even be possible to win a curing substance from his blood. To test this idea, he keeps an infected man like a wild animal in his cellar. However, the time flies and Neville doesn’t succeed in making contact with other healthy people. When his loyal sheepdog is bitten, he has to kill him. His desperation finally overcomes him. By chance, he finds two other people who were immune, Anna and Ethan (Alice Braga and Charlie Tahan). Dr. Neville enables them to escape into a coal shaft.

Afterwards of course with the blood of the infected experimental subject in which the antidote is and sprinkles himself with the attackers in the air.
Ich habe leider keine Ahnung, was du hier ausdrücken willst. :)

Anna and Ethan find their way to a colony of survivors. There they hand over the antidote which signifies the rescue of the humanity.

Ein Virus ist "it", nach Doppelpunkten schreibt man im Englischen immer klein weiter. Bei Personen benutzt man in Relativsätzen "who", bei Dingen/Sache "which". Manchmal drückst du dich ein bisschen unidiomatisch aus - z.B. muss es "by chance" heißen und nicht "from chance". Dein Satzbau ist z.T. ein bisschen "deutsch" - ansonsten alles bestens. :)