it looks like it was originally created in 2018 so I don't think the anti-vax implications were intentional (though unfortunate with hindsight). I think this is more of a combination of personifying growing older and conforming to social expectations as women (marrying men, working corporate jobs) as "zombies" and the girls choosing to die to not "become like them". Hence the final page being people reading a newspaper on a packed train, presumably commuting to work discussing their suicide. It's a bit bleak but I don't think it's malicious.