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Over the past century, many notable viruses have emerged from animals to cause widespread illness and death in people. The list includes the pathogens behind pandemic influenza, Ebola, Zika, West Nile fever, SARS, and now COVID, brought on by the virus SARS-CoV-2. For all of these microbes, the animal species that served as the original source of spillover was hard to find. And for many, that source still has not been conclusively identified. Confirming the circumstances and key participants involved in the early emergence of an infectious disease is a holy grail of this type of scientific inquiry: difficult to track and even more difficult to prove. (Christine K. Johnson, 6/9)

The coronavirus pandemic seems to be in a state of quantum superposition. Like Schrödinger’s cat, it is both alive and dead, depending on who’s looking.In the U.S. and U.K., where large numbers of people have been vaccinated, it seems mostly dead. Not dead-parrot dead, but at least changing from Schrödinger’s tiger to Schrödinger’s unfriendly house cat that scratches up the furniture and also you’re allergic. (Mark Gongloff, 6/9)

As variants of Covid-19 have spread in the US, the public health policy and programmatic responses have been largely consistent: vaccinate as soon as possible, mask up and keep social distancing. But as vaccinations have increased, there has been a collective relaxation of the masking and distancing that were previously indispensable public health measures. While this may seem like an intuitive first step toward a post-vaccination "normal," we must be conscious of the Delta variant (B.1.617.2), which first devastated India, and still poses a major international health threat. (David Holtgrave, 6/10)

As nations race to roll out vaccines in the global effort to contain Covid-19 and allow for a return to normal, the rise of dangerous virus variants threatens to prolong the pandemic. In the U.K., the spread of the so-called delta variant, first identified in India, has led officials to send military personnel to hotspots and prompted the government to reconsider easing Covid restrictions on June 21 as planned. Here, Sam Fazeli, a Bloomberg Opinion contributor who covers the pharmaceutical industry for Bloomberg Intelligence, answers questions about the risks stemming from this variant and more. The conversation has been edited and condensed. (Sam Fazeli, 6/9)

What does “reopening” mean in a place that for the most part never closed? When covid-19 struck, the residents of Ohio’s 32 Appalachian counties weren’t particularly panicked or anxious to embrace restrictions — which made them objects of contempt for much of the country. It also meant their daily lives were barely disturbed, since the big-box grocery, retail and hardware stores where they typically congregated never closed, and many local restaurants reopened quickly at “limited capacity,” which meant the usual crowd. Like everywhere, many of them caught covid-19 and most of them recovered. But some — 3,870 so far in the 32 counties — died. (Gary Abernathy, 6/9)

The SARS-CoV-2 virus presented the world with a host of clinical challenges, not least its rapid transmission rate and ability to mutate into new, possibly even more contagious variants. New vaccines, therapeutics, and diagnostics had to be tested under unusual and unpredictable circumstances; the most promising studies weren’t necessarily prioritized for high-quality clinical trials and competed for study participants; pandemic waves swept across the globe without real-time data; and feedback from health authorities varied significantly from one part of the world to the next. (John Tsai, 6/10)

In the years after the Civil War, smallpox spread throughout the South, mainly infecting Black people. The story of an outbreak of a disease long since eradicated may seem remote from our own times. But the smallpox epidemic of the 1860s offers us a valuable, if disconcerting, clue about how epidemics end. (Jim Downs, 6/9)