evidence: Confusing mask guidance. Although face masks are now widely considered a crucial part of stopping transmission, U.S. and global health authorities were slow to recommend them for public use. Many countries in East and Southeast Asia, including China and Japan, had normalized mask wearing well before the pandemic—in part because of the SARS outbreak in 2002–2003. Unlike the SARS virus, however, scientists now know that SARS-CoV-2 often spreads before a carrier develops symptoms (and possibly even if they never do). In the early weeks and months of the COVID outbreak, the CDC and WHO stated that face masks were not necessary for the general public unless a person was experiencing symptoms or caring for someone who was. The agencies also initially urged people not to buy high-filtration N95 and surgical masks because they were needed for health care workers and were in short supply because of inadequate government stockpiles. Though perhaps well-meaning, the WHO’s and CDC’s guidances sent a mixed message about masks’ effectiveness—and about who deserves protection. The CDC changed course and recommended cloth face coverings in April. The WHO did not do so until June, citing inadequate evidence of their efficacy before then. The CDC did not respond to a request for comment, and the WHO referred Scientific American to press briefings that addressed these issues. In these briefings, experts pointed to a lack of high-quality evidence for mask use. The WHO’s director general also stated that, in the absence of other public health measures, "masks alone will not protect you from COVID-19."