1stly you should continue occupational therapy and speech therapy if possible via video calls. And about the hand hygiene and all no kid his age would understand the meaning of all those things so don't worry
Next Steps
Just avoid meeting people unnecessarily
Keep your house and surroundings clean
continue with whatever treatment is going on howmuchever is possible at home and decrease frequency of visits to the centre like go once a week instead of 3 times a week
There are no immune boosters but give multivitamins
SYP.BEVON 5ML ONCE A day for 3.to 6 months