As his respiration became shallow, it means that he is going to have difficulty in breathing, so it is best to have a device or assistance to be placed on him, in order to assist his breathing and ventilation. It is best to insert an airway adjuct to him, in order for his breath to widen and to insert a bag mask device, to assist his ventilations.
Out of the following choices, the best treatment for a virus is is an antibiotic. However, most virus's can't be treated with an antibiotic and will be treated with over the counter remedies.