This is the editor’s letter in the current issue of The Week magazine.

Viruses, strictly speaking, are not alive. They are tiny sets of genes bundled within protein shells, with one singular function — to replicate. Lacking cells or other common features of living organisms, viruses are parasitic zombies. They infect living cells, hijack the genetic machinery, and mass-produce replicas of themselves. (A single sneeze can release 100,000 viruses into the air.) The common cold is a virus, and so are influenza, measles, HIV, and Ebola. The new coronavirus, Covid-19, has joined the list of humanity's viral scourges, after apparently jumping species from its original host, bats. It has sickened more than 80,000 people and, infectious-disease experts say, it's coming to America. One way or another, it will affect all of our lives.

As Covid-19 relentlessly advances, there is much scientists and doctors do not yet understand. Infection produces widely varying responses. Some people have no symptoms, but can still transmit the virus to others. A majority suffer only mild respiratory distress. Others become severely sick, with flu-like aches and high fever and pneumonia. Deaths occur when the infections trigger an out-of-control immune response, creating a "cytokine storm" that inflames and shuts down the lungs. Scientists estimate a mortality rate of 2 to 3 percent. If there are major outbreaks in the U.S., authorities may discourage people from congregating in crowds, and may temporarily shut schools and curtail travel. The economy could take a significant hit. Covid-19 may even have an unpredictable impact on the presidential race. Americans tend to overreact to such disruptions; protected by our oceans and relative affluence, we expect to be exempt from problems affecting places like China and Italy. Now we face a mindless invader thousands of times smaller than a grain of sand — one that knows no national boundaries. Covid-19 will test our strength, our social cohesion, and our leaders.