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An estimated\n                    <jats:italic>R<\/jats:italic>\n                    \u2009=\u2009\n                    <jats:italic>1<\/jats:italic>\n                    is universally interpreted as a stability threshold distinguishing epidemic growth (\n                    <jats:italic>R<\/jats:italic>\n                    \u2009&gt;\u2009\n                    <jats:italic>1<\/jats:italic>\n                    ) from control (\n                    <jats:italic>R<\/jats:italic>\n                    \u2009&lt;\u2009\n                    <jats:italic>1<\/jats:italic>\n                    ). We demonstrate that this interpretation frequently fails because\n                    <jats:italic>R<\/jats:italic>\n                    typically averages over groups with heterogeneous characteristics. We find that\n                    <jats:italic>R<\/jats:italic>\n                    \u2009=\u2009\n                    <jats:italic>1<\/jats:italic>\n                    conceals valuable early-warning signals of resurgence and misclassifies complex dynamics as noise, generating false positive stability thresholds that diminish predictive and policymaking value. We further illustrate that a popular alternative transmissibility definition (using next-generation matrices) overcorrects this issue, producing false negative stability signals by amplifying stochastic variation. We address these limitations by adapting a recently developed statistic,\n                    <jats:italic>E<\/jats:italic>\n                    , derived from\n                    <jats:italic>R<\/jats:italic>\n                    using experimental design theory. We show that\n                    <jats:italic>E<\/jats:italic>\n                    tightly constrains the set of scenarios consistent with stability, while remaining robust to noise and establish\n                    <jats:italic>E<\/jats:italic>\n                    \u2009=\u2009\n                    <jats:italic>1<\/jats:italic>\n                    as a more practical and meaningful real-time threshold.\n                  <\/jats:p>","DOI":"10.1038\/s42005-026-02631-6","type":"journal-article","created":{"date-parts":[[2026,4,15]],"date-time":"2026-04-15T11:46:30Z","timestamp":1776253590000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["The R\u2009=\u20091 threshold can misclassify epidemic stability"],"prefix":"10.1038","volume":"9","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7806-3605","authenticated-orcid":false,"given":"Kris V.","family":"Parag","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mauricio","family":"Santillana","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Anne","family":"Cori","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Uri","family":"Obolski","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,4,15]]},"reference":[{"key":"2631_CR1","unstructured":"Anderson, R. et al. 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