It means that the school will be closed for year nine (aged 13 and 14) pupils tomorrow (Friday) and Monday.
Head teacher Sarah Findlater said the number of absent staff made the normal running of the school difficult.
In a letter to parents, she said: ‘Please be assured that this decision has not been taken lightly. We have tried to do everything to avoid this scenario, and despite high levels of staff absence for much of this term, we have coped, with no year groups being asked to remain at home since the second week of January.’
She added that, where possible, staff would inform the students of the work that should be completed while they are at home, but with such a significant number of the teaching workforce absent, this would not be possible in all cases.
All other pupils should go to school as normal.
The situation at Ramsey Grammar School comes days after Ballakermeen High School in Douglas sent some pupils home because of a similar problem.