The number of infections today was double that of yesterday.
There were twice as many new cases today compared to yesterday.
Today, the number of new cases doubled from yesterday.
こんにちは。
様々な表現の仕方があると思いますが、例えば下記のような言い方はいかがでしょうか:
・The number of infections today was double that of yesterday.
今日の感染者数は昨日の2倍でした。
・There were twice as many new cases today compared to yesterday.
今日は、昨日に比べて2倍の新規感染が確認されました。
・Today, the number of new cases doubled from yesterday.
今日、新規件数は昨日から2倍にになった。
new cases(新規症例)や positive cases(陽性症例)などは最近のニュースでよく見る表現です。
ぜひ参考にしてください。