Our understanding of Covid-19 as a disease has evolved rapidly over the course of the pandemic. While many aspects of Covid-19from its symptoms to its duration to its short- and long-term aftereffectsremain difficult to pin down, we now have enough data to identify four broad stages of infection that can guide us going forward.
To grasp the complete picture, it helps to look back on how each individual piece of the puzzle fell into place. The story began, like most mysteries, with an emerging problem and a complete lack of knowledge. In the first few weeks of the outbreak, Covid-19 appeared to be nothing more than a serious pneumonia. Symptom-wise, it seemed similar enough to what some people experience when they contract a severe case of the flu.
A month went by. Researchers in China, and soon enough elsewhere, began to realize that the lung damage associated with the disease was more complex than previously thought. This was due in large part to an overreaction of the immune system known as a cytokine storm. Not only was the pathology of autospied lungs atypical for viral-induced pneumonia, but high levels of inflammatory chemokine and cytokines were present as well.