Normally, the lungs collect oxygen in tiny air sacs called the alveoli before transferring it to the bloodstream. However, if the lungs are inflamed, this supply of air to the bloodstream is slowed down or limited.
Infection and condition
Patients infected by Covid-19 usually develop pneumonitis or lung inflammation and must rely on a ventilator to help them breathe. Patients with a lower level of infection also develop pneumonitis, though they do not need a ventilator and can usually recover on their own.