BOSTON — New research suggests the protection the Moderna vaccine gives against COVID-19 lasts for at least six months. The report Tuesday in the New England Journal of Medicine echoes what Pfizer said last week about its vaccine, which works in a similar way. Both reports were based on follow-up tests in dozens of people who received the shots during studies that led to the vaccines’ use. Those studies were done before troubling new variants, or versions of the coronavirus, had emerged and started to spread. A separate report in the medical journal adds to concern about the variants. Scientists...