What experts say about whether it's time to relax mask-wearing rules outdoors; the 12 big, unanswered questions about Covid-19; and more.

More than half of US adults have gotten a vaccine. So why are coronavirus cases still rising? (Monday, April 19)

Even though more than half of American adults have received at least one dose of a Covid-19 vaccine, coronavirus cases are still rising throughout much of the United States—and hospitalizations of younger adults are increasing significantly.

Do Covid-19 vaccines affect women differently? 5 key questions, answered. (Tuesday, April 20)

As Covid-19 vaccines roll out nationwide, experts are exploring whether the vaccines might affect women differently than men—and what implications that might have for mammograms, blood clot risks, vaccine side effects, menstrual cycles, and more.

The 12 big, unanswered questions about Covid-19 (Wednesday, April 21)

Even now, more than 16 months into this pandemic, "many key questions about SARS-2 and the disease it causes, Covid-19, continue to bedevil scientists," Helen Branswell writes for STAT News.

What if America never reaches herd immunity? (Thursday, April 22)

Public officials have long suggested the Covid-19 epidemic will end when America reaches so-called "herd immunity"—but now, with a sizable fraction of U.S. residents saying they won't get vaccinated, some experts worry herd immunity may be impossible. Here's what that could mean for the epidemic's future.

Is it time to relax mask-wearing rules outdoors? Here's what experts say. (Friday, April 23)

Even as many states continue to mandate mask-wearing both indoors and outdoors, a growing body of evidence suggests outdoor coronavirus transmission is extremely rare. Here's what the evidence says—and one expert's "two-out-of-three rule" for guiding her own mask-wearing decisions.