YOU SAID:
I am really sad because today my dog has to get vaccinated
INTO JAPANESE
今日私の犬は予防接種を受けなくてはなっているので、私は本当に悲しいです
BACK INTO ENGLISH
I'm really sad because today my dog has to be vaccinated
INTO JAPANESE
今日私の犬は予防接種を受けなければならないので、私は本当に悲しいです
it is unlikely that this phrase will ever reach equilibrium