As the CDC urges Americans to mask up against the Delta variant, Sweden’s chief epidemiologist has argued that more data is needed about the strain’s infectiousness. His mask-free nation is hovering at zero Covid deaths per day. Anders Tegnell said on Friday that there was “a lot we do not know” about Delta and cautioned against drawing “far-reaching conclusions” about the coronavirus strain. He noted that the variant had been circulating in Sweden “for quite some time” with little effect, particularly in high-risk settings such as nursing homes. His comments were made in response to newly released data from the...