>>718142114
Not really, at least from what's presented to you.
>1. It's implied they tried this shit before with others and it didn't fully work so instead of trying to breed Ellie they immediately jump the gun
>2. Vaccine wouldn't really do much aside from maybe provide a small safety net. Infected can still kill you the old fashioned way and that's probably the more likely outcome in a bad encounter with em anyway
>3. Even if we assume magic "just trust me bro they would've created it" meta narrator affirmation, development and distribution of said vaccine would've been a logistical nightmare at that point. Besides the world had basically adapted/moved on already.
>4. Based on everything we see and hear about the Fireflies (including in game collectibles) its repeatedly shown they are colossal incompetent fucking retards who tend to make things worse wherever they go. Most likely scenario if they did make a vaccine/cure would be to use it as a mean for power only to end up getting bulldozed by other factions the second they learned they had it. This would most likely result in the vaccine getting destroyed in the struggle and make it all for nothing because they are retards.