Is eating kefir good for covid ? what vitamins should i give to my teenage son who tested positive for covid ?

To my knowledge, there is very little information, based on studies. Maintain a healthy diet, including antioxidant and Vit C rich foods, lean protein and keep him well hydrated. If he is otherwise healthy, most patients recover well, but Long COVID and MIS C are known complications. Watch for signs of shortness of breath and prolonged cough. Vaccination is still recommended.