This subject line appears to be a romaji rendering of a Japanese phrase: → "Only my vaccine can save a world that has become zombie-like / turned into zombies."
Only my vaccine can save the world that has become zombie. orenowakuchindakegazombieshitasekaiwosukueru
Within six months, 94% of the global population had turned. The remaining 6% retreated to subterranean bunkers and mountain fortresses. possibly an anime
Ren wept. "I can't save them permanently. But I can use the lucid window to implant a second vaccine—one that rewrites the implant's firmware mid-infection." or a light novel.
It appears to be a sentence or a title from a Japanese media, possibly an anime, manga, or a light novel.