Yes drinking calamansi juice daily is good for the flu.
The juice calamansi juice contains many minerals and nutrients as well as Vitamin C which is good for boosting your bodies immune system.
So by drinking a cup or two of calamansi juice before you get the flu or cold can help prevent the cold or flu from infecting your body because your bodies immune system will be built up and improved.
You still might get the flu or cold but when you increase your Vitamin C intake it makes it harder for your body to be infected by the cold or flu virus and if you do get infected by the cold or flu virus it may not last as long.
Drinking orange juice as well as eating oranges a few times per week or even eating some calamansi fruit can help boost your immune system to prevent the flu or cold virus and help get rid of the cold or flu virus much sooner.
Getting plenty of rest and exercise and overall eating healthy can go a long way at getting rid of the flu and preventing the flu or cold virus from infecting you.
If you haven't gotten a flu shot before the flu season I highly recommend you do so because it can help prevent the flu.