The <a href="https://en.wikipedia.org/wiki/World_Health_Organization" id="mwAbU" rel="mw:WikiLink" title="World Health Organization">World Health Organization</a> is informed of cases of pneumonia with an unknown cause, detected in <a href="https://en.wikipedia.org/wiki/Wuhan" id="mwAbY" rel="mw:WikiLink" title="Wuhan">Wuhan</a>.<sup about="#mwt114" class="mw-ref reference" data-mw='{"name":"ref","attrs":{},"body":{"id":"mw-reference-text-cite_note-20"}}' id="cite_ref-20" rel="dc:references" typeof="mw:Extension/ref"><a href="./December_31#cite_note-20" id="mwAbc" style="counter-reset: mw-Ref 20;"><span class="mw-reflink-text" id="mwAbg">[20]</span></a></sup> This later turned out to be <a href="https://en.wikipedia.org/wiki/COVID-19" id="mwAbk" rel="mw:WikiLink" title="COVID-19">COVID-19</a>, the cause of the <a href="https://en.wikipedia.org/wiki/COVID-19_pandemic" id="mwAbo" rel="mw:WikiLink" title="COVID-19 pandemic">COVID-19 pandemic</a>.<sup about="#mwt118" class="mw-ref reference" data-mw='{"name":"ref","attrs":{},"body":{"id":"mw-reference-text-cite_note-21"}}' id="cite_ref-21" rel="dc:references" typeof="mw:Extension/ref"><a href="./December_31#cite_note-21" id="mwAbs" style="counter-reset: mw-Ref 21;"><span class="mw-reflink-text" id="mwAbw">[21]</span></a></sup>
<span class="mw-reference-text" id="mw-reference-text-cite_note-20"><cite about="#mwt111" class="citation web cs1" id="mwCAg"><a class="external text" href="https://www.who.int/csr/don/05-january-2020-pneumonia-of-unkown-cause-china/en/" id="mwCAk" rel="mw:ExtLink nofollow">"Pneumonia of unknown cause – China"</a>. <i id="mwCAo">WHO</i>.</cite><span about="#mwt111" class="Z3988" id="mwCAs" title="ctx_ver=Z39.88-2004&amp;rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&amp;rft.genre=unknown&amp;rft.jtitle=WHO&amp;rft.atitle=Pneumonia+of+unknown+cause+%E2%80%93+China&amp;rft_id=https%3A%2F%2Fwww.who.int%2Fcsr%2Fdon%2F05-january-2020-pneumonia-of-unkown-cause-china%2Fen%2F&amp;rfr_id=info%3Asid%2Fen.wikipedia.org%3ADecember+31"></span></span>