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摘要

The story of the war against Covid-19 begins half a billion years ago. That's when jawed fish-our scaly forebears-evolved an immune system capable of learning, adapting, and defeating invaders. The adaptive immune system, as it's called, was so massive an improvement over the slow-learning innate immune system of the day that some scientists now describe it as the Big Bang of immunology. In humans, only the brain rivals the immune system's sophistication, says Alice Huang, a senior faculty associate at the California Institute of Technology who has studied virus-host interactions for five decades. "It is a complex interplay between cells and their products." As awesome as our immune system is, though, it doesn't win every time. Right now it's facing a stern challenge from a foe it doesn't always know how to fight. While some countries have managed to control the coronavirus through social measures such as mask-wearing, others-notably the U.S.-have manifestly failed. According to the World Health Organization, Covid-19 has killed almost 700,000 people and sickened some 18 million since its identification in Wuhan, China, last December.