Translation:He had a serious accident and is now in the hospital.
FYI to any students of English here: outside of the USA, 'in the hospital' means inside the hospital building. 'He's in the hospital' presumably means he's visiting someone, or perhaps he works there. It's roughly equivalent to 'He's at the hospital.' 'In hospital' means the subject has been admitted as a patient, probably for a stay of at least one night. 'He's in hospital' means he's had an accident or is sick. We cannot here use 'in the' or 'at the'. In American English 'in the hospital' does double duty for both senses. Incidentally, without a stated time, the tense in the first clause should be 'He's had [he has had] an accident', not 'he had', though again in informal US English the present perfect is dispensed with. Both variants are accepted by Duolingo now.