The pandemic of the Spanish flu ended in around three years, so I did not think that this corona pandemic would last so long, especially in this age of advanced medicine.
ご質問ありがとうございます。
"The pandemic of the Spanish flu ended in around three years,"＝「スペイン風邪の流行は3年ほどで終わった」
"so I did not think that this corona pandemic would last so long,"＝「なのでこのコロナの流行がこれほど長引くとは思いませんでした」
"especially in this age of advanced medicine."＝「特にこの医療が進歩した時代に。」
ご参考に。
Even the Spanish flu only lasted about three years, so I didn't think the Corona virus would go on and on the way it has, especially in light of the fact that medicine has advanced as much as it has.
この場合、次のような言い方ができますよ。
ーEven the Spanish flu only lasted about three years, so I didn't think the Corona virus would go on and on the way it has, especially in light of the fact that medicine has advanced as much as it has.
「スペイン風邪は約3年で収まったから、コロナがこんなに長引くと思わなかった。特に、医療がこれほど進んでいる事実を照らし合わせるとね」
in the light of the fact that ...で「... という事実を照らし合わせると」
ご参考まで！
アメリカ合衆国 
カナダ 
