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Will summertime slow the virus that causes Covid-19, as it has done with many other viruses that sow flu, colds and pneumonia? A new study finds that it may, though not enough to wipe out the pathogen or keep the pandemic from resurging in the fall. The study, done by ecological modelers at the University of Connecticut, understands the main natural weapon against the novel germ to be ultraviolet light — an invisible but energetic part of the sun’s electromagnetic spectrum that’s well-known for damaging DNA, killing viruses and turning healthy human skin cells into cancerous ones. (Broad, 4/24)

As the novel coronavirus swept through communities around the world, preying disproportionately on the poor and the vulnerable, one disadvantaged group has demonstrated a remarkable resistance. Women, whether from China, Italy or the U.S., have been less likely to become acutely ill — and far more likely to survive. Which has made doctors wonder: Could hormones produced in greater quantities by women be at work? Now scientists on two coasts, acting quickly on their hunches in an effort to save men’s lives, are testing the hypothesis. The two clinical trials will each dose men with the sex hormones for limited durations. (Rabin, 4/27)

The World Health Organization on Saturday said there was not enough evidence that a person who has recovered from covid-19 is immune from a second infection. This comes as the known coronavirus death toll worldwide surpassed 200,000, though the true figure is unknown. (4/26)

Many patients with severe cases of Covid-19 have been shown to have extremely low levels of oxygen in the blood. Others who have tested positive find themselves experiencing shortness of breath. Perhaps that's why people are so interested lately in pulse oximeters, medical devices that measure the saturation of oxygen in red blood cells. (Kaur, 4/26)

Back in the early 20th century, the baseball pitcher Walter Johnson confounded opposing batters by throwing the fastest fastball they’d ever seen. “You can’t hit what you can’t see,” they would say. A century later, it’s an apt saying for those navigating this unusual moment. The surreptitious and the invisible are defining the human landscape during these weeks in ways we are only barely beginning to understand. (Anthony, 4/27)

An analysis by doctors at Children’s National Hospital in Washington calls into question the commonly held — and comforting — assumption that children seem to escape the novel coronavirus’s more serious impacts. “We have been ready, but frankly, surprised,” Roberta DeBiasi, the hospital’s infectious disease division chief, said Friday. “We are actually having a significant number of admissions and critical care admissions.” (Swenson, 4/25)