�������ýҕ�l

The first confirmed coronavirus infections in Europe and the United States, discovered in January, did not ignite the epidemics that followed, according to a close analysis of hundreds of viral genomes. Instead, the outbreaks plaguing much of the West began weeks later, the study concluded. The revised timeline may clarify nagging ambiguities about the arrival of the pandemic. For example, while President Trump has frequently claimed that a ban on travelers from China prevented the epidemic from becoming much worse, the new data suggest that the virus that started Washington State’s epidemic arrived roughly two weeks after the ban was imposed on Feb. 2. (Zimmer, 5/27)

There’s a good chance the coronavirus will never go away. Even after a vaccine is discovered and deployed, the coronavirus will likely remain for decades to come, circulating among the world’s population. Experts call such diseases endemic — stubbornly resisting efforts to stamp them out. Think measles, HIV, chickenpox. (Wan and Johnson, 5/27)

The coronavirus still has a long way to go. That’s the message from a crop of new studies across the world that are trying to quantify how many people have been infected. Official case counts often substantially underestimate the number of coronavirus infections. But even in results from a new set of studies that test the population more broadly to estimate everyone who has been infected, the percentage of people who have been infected so far is still in the single digits. (Popovich and Sanger-Katz, 5/28)

Try out this riddle: If you could double over a piece of normal notebook paper 42 times, how thick would it be? The answer, though fanciful, illustrates just how hard it can be to understand exponential growth and doubling, two pieces of math that explain the spread of viruses like Covid-19. Because by the time you made the 42nd fold, your stack of paper would reach the moon. It's not just a handy fact for trivia night: It shows how exponential growth can result in numbers that are nearly incomprehensible. (Smith, 5/28)

Fears about catching the coronavirus from contaminated surfaces have prompted many of us to spend the past few months wiping down groceries, leaving packages unopened and stressing about touching elevator buttons. But what’s the real risk of catching Covid-19 from a germy surface or object? The question has been on people’s minds lately, and there was some confusion after the Centers for Disease Control and Prevention made some edits to its website last week. (Parker-Pope, 5/28)

National Institutes of Health Director Francis Collins said the coronavirus is “absolutely not" manmade but he could not rule out the idea that it escaped from a lab in Wuhan, China, where the first known cases emerged. “Whether [the coronavirus] could have been in some way isolated and studied in this laboratory in Wuhan, we have no way of knowing,” he told POLITICO on Wednesday. (Brennan, 5/27)

A research letter published yesterday in JAMA revealed a 3.9% prevalence of COVID-19 among women giving birth at three Yale New Haven hospitals in Connecticut. A separate study published today in Infection Control & Hospital Epidemiology found a 7.9% prevalence of the novel coronavirus among symptomatic obstetric patients and a 1.5% prevalence among asymptomatic patients (those not having COVID-19 symptoms) at four Boston hospitals. (VAn Beusekom, 5/27)

Improving symptoms, no fever for 3 days, at least 10 days since symptom onset—those are criteria for when the Centers for Disease Control and Prevention (CDC) says people with COVID-19 can leave self-quarantine and be around others again. The guidance was released earlier this week and will prove helpful as states continue to open up and people return to work. The CDC also said asymptomatic people who have tested positive for COVID-19 should wait 10 days after the positive test before resuming normal activities. (Soucheray, 5/27)