A meta-analysis published by the journal JAMA Network Open in December 2020 found that less than 1% of people with asymptomatic or pre-symptomatic Covid-19 infect other members of their households. These results led the authors to remark that "the lack of substantial transmission from observed asymptomatic index cases is notable." An August 2020 paper in the journal Nature Medicine explains that worries about widespread transmission of C-19 by asymptomatic and pre-symptomatic people stemmed from models, and real-world observations from "direct contact tracing studies" have proven that the actual threat is "lower than that predicted by Covid-19 transmission models."