A lot of serious side effects from the COVID-19 immunization have been reported.
There have been many reports of severe side effects from the COVID-19 vaccination.
ーA lot of serious side effects from the COVID-19 immunization have been reported.
「コロナワクチン接種のたくさんの重大な副反応が報告されている」
serious side effects で「重大な副作用・副反応」
COVID-19 immunization で「コロナワクチン接種」
ーThere have been many reports of severe side effects from the COVID-19 vaccination.
「コロナワクチン接種の重大な副反応が多数報告されている」
severe side effects で「重大な副作用・副反応」
COVID-19 vaccination で「コロナワクチン接種」
ご参考まで！
カナダ 
