Having watched the trailer, I have a theory about who the
actual main protagonist is going to be.
From the outset, I think everyone believes that Katherine Waterston's character is going to be the main protagonist of this film - going by some of the production shots, press releases and a few other tidbits.
However, I think Ridley is being clever about it, and that he might have a trick or two up his sleeves.
I actually think that....
Spoiler
Carmen Ejogo's character is going to be the main protagonist. We see in the trailer she is trapped in quarantine with the crew member and the "backburster" - the other crew member won't let her out of quarantine. We then see a shot of Carmen Ejogo's character in the same room, holding a blade, sitting up on the counter presumably defending herself against whatever has burst out of the guy's back.
My reasoning - I think Ridley has been clever by not showing too much of her. We've only seen her once in the trailer, and the only time we have is with her facing conflict, and showing fight by defending herself. Then nothing else. The focus then is on Katherine Waterston's character.
I have a feeling that Ridley is going to give us the impression of Katherine Waterston's character being the main protagonist probably for at least a third/half of the movie, before being unexpectedly killed. Then Ejogo's character will emerge, possibly after it being hinted at that she has been killed first.
It might not turn out to be true, but really have a feeling that's what Ridley has planned.