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me had saved as By that summer, dexamethasone had become the primary treatment for severe COVID, having been found to reduce mortality among hospitalized patients by up to a third.4 Dexamethasone, a steroid that has been in use since the 1950s, works on COVID somewhat counterintuitively: by suppressing some of the immune system's defenses. Why would you want to suppress your immune system? Because once you're past the early stages of infection, the biggest danger of COVID doesn't actually come from the virus, it comes from the immune system reaction that's triggered by the virus. In most people, the immune system is able to reduce the amount of virus within five or six days of getting infected, but the it becomes so activated that it can cause a phenomenon known as a cytokine storm--a flood of signals to send massive amounts of fluids and blood to various organs, which in turn can cause organ failure and death. It's your body's overreaction to the invasion that makes you sick. Dexamethasone was a significant success: It was effective, easy to deliver, cheaper than any of the alternatives, and widely available even in many developing countries. (In fact, even before COVID, the WHO deemed it an essential medicine for use in pregnant women.) Less than a month after it was shown to work well, a nonprofit called the African Medical Supplies Platform had acquired 9 million tablets that would be available free for every country in the African Union.5 British researchers estimated that by March 2021, dexamethasone had saved as many as one million lives around the world.6 Even so, the drug does have its downsides--chiefly, that if used too early, it will mute your immune response at the very moment when it needs to be at full strength so it can stop the virus from replicating. When that happens, you become more susceptible to complications and