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<article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" dtd-version="1.3" xml:lang="en" article-type="letter"><?properties open_access?><processing-meta base-tagset="archiving" mathml-version="3.0" table-model="xhtml" tagset-family="jats"><restricted-by>pmc</restricted-by></processing-meta><front><journal-meta><journal-id journal-id-type="nlm-ta">Emerg Infect Dis</journal-id><journal-id journal-id-type="iso-abbrev">Emerg Infect Dis</journal-id><journal-id journal-id-type="publisher-id">EID</journal-id><journal-title-group><journal-title>Emerging Infectious Diseases</journal-title></journal-title-group><issn pub-type="ppub">1080-6040</issn><issn pub-type="epub">1080-6059</issn><publisher><publisher-name>Centers for Disease Control and Prevention</publisher-name></publisher></journal-meta>
<article-meta><article-id pub-id-type="pmid">38146992</article-id><article-id pub-id-type="pmc">10756379</article-id><article-id pub-id-type="publisher-id">23-1487</article-id><article-id pub-id-type="doi">10.3201/eid3001.231487</article-id><article-categories><subj-group subj-group-type="heading"><subject>Letters to the Editor</subject></subj-group><subj-group subj-group-type="article-type"><subject>Letters to the Editor</subject></subj-group><subj-group subj-group-type="TOC-title"><subject>SARS-CoV-2 Incubation Period during Omicron BA.5&#x02013;Dominant Period, Japan (Response)</subject></subj-group></article-categories><title-group><article-title>SARS-CoV-2 Incubation Period during Omicron BA.5&#x02013;Dominant Period, Japan (Response)</article-title><alt-title alt-title-type="running-head">SARS-CoV-2 Incubation Period during Omicron BA.5&#x02013;Dominant Period, Japan (Response)</alt-title></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><name><surname>Ogata</surname><given-names>Tsuyoshi</given-names></name></contrib><contrib contrib-type="author"><name><surname>Tanaka</surname><given-names>Hideo</given-names></name></contrib><aff id="aff1">Itako Public Health Center of Ibaraki Prefectural Government, Ibaraki, Japan (T. Ogata); </aff><aff id="aff2">Public Health Center of Neyagawa City, Osaka, Japan (H. Tanaka)</aff></contrib-group><author-notes><corresp id="cor1">Address for correspondence: Tsuyoshi Ogata, Itako Public Health Center of Ibaraki Prefectural Government, Osu1446-1, Itako, Ibaraki 311-2422, Japan; email: <email xlink:href="kenkoukikikanri@gmail.plala.or.jp">kenkoukikikanri@gmail.plala.or.jp</email></corresp></author-notes><pub-date pub-type="ppub"><month>1</month><year>2024</year></pub-date><volume>30</volume><issue>1</issue><fpage>207</fpage><lpage>207</lpage><permissions><copyright-year>2024</copyright-year><license><ali:license_ref xmlns:ali="http://www.niso.org/schemas/ali/1.0/" specific-use="textmining" content-type="ccbylicense">https://creativecommons.org/licenses/by/4.0/</ali:license_ref><license-p>Emerging Infectious Diseases is a publication of the U.S. Government. This publication is in the public domain and is therefore without copyright. All text from this work may be reprinted freely. Use of these materials should be properly cited.</license-p></license></permissions><related-article related-article-type="commentary-article" id="ra1" xlink:href="38146992" ext-link-type="pubmed" journal-id="Emerg Infect Dis" vol="30" page="206"><string-name><surname>Cheng</surname><given-names>H</given-names>
</string-name>, <string-name><surname>Akhmetzhanov</surname><given-names>AR</given-names>
</string-name>, <string-name><surname>Dushoff</surname><given-names>J</given-names>
</string-name>. <article-title>SARS-CoV-2 incubation period during Omicron BA.5&#x02013;dominant period, Japan.</article-title>
<source>Emerg Infect Dis</source>. <year>2024</year>;<volume>30</volume>:<fpage>206</fpage>&#x02013;<lpage>7</lpage>. <pub-id pub-id-type="doi">10.3201/eid2903.221360</pub-id></related-article><kwd-group kwd-group-type="author"><title>Keywords: </title><kwd>COVID-19</kwd><kwd>respiratory infections</kwd><kwd>severe acute respiratory syndrome coronavirus 2</kwd><kwd>SARS-CoV-2</kwd><kwd>SARS</kwd><kwd>incubation period</kwd><kwd>Omicron</kwd><kwd>BA.5</kwd><kwd>coronavirus disease</kwd><kwd>zoonoses</kwd><kwd>viruses</kwd><kwd>coronavirus</kwd><kwd>Japan</kwd></kwd-group></article-meta></front><body><p><bold>In Response:</bold> We thank Dr. Cheng and colleagues (<xref rid="R1" ref-type="bibr"><italic>1</italic></xref>) for their valuable comments regarding our study of incubation periods observed for the SARS-CoV-2 Omicron BA.5 subvariant in Japan (<xref rid="R2" ref-type="bibr"><italic>2</italic></xref>). As we indicated in our study limitations paragraph, &#x0201c;patient pairs with long incubation periods might be censored during observational periods, and selection bias might result in underestimation&#x0201d; (<xref rid="R2" ref-type="bibr"><italic>2</italic></xref>). We have several other comments to make regarding our study. First, our previous study during the increasing dominance of the Omicron BA.1 subvariant only included patients who had 1 exposure day; we reported incubation periods of 3.0 days for L452R mutation&#x02013;negative patients and 3.3 days for unvaccinated patients (<xref rid="R3" ref-type="bibr"><italic>3</italic></xref>), which was similar to 3.2 days reported in a study of patients with BA.1 infections who had multiple exposure days (<xref rid="R4" ref-type="bibr"><italic>4</italic></xref>). Therefore, the effect of only including patients who had 1 exposure day should be further evaluated. Second, the incubation period for the BA.5 subvariant in our study was 3.0 days for patients with infectors who were &#x02264;19 years of age and 2.1 days for patients with infectors who were &#x02265;60 years of age (<xref rid="R2" ref-type="bibr"><italic>2</italic></xref>). Because those data are considerably different, adjustment for demographic factors for both infectors and infectees might be necessary to compare incubation periods. Third, although including patients with multiple exposure days decreases selection bias, it might increase uncertainty regarding the actual time of infection (<xref rid="R5" ref-type="bibr"><italic>5</italic></xref>). Therefore, comparing incubation periods in studies that use various methods and evaluating corresponding study limitations are useful for review and discussion.</p></body><back><fn-group><fn fn-type="other"><p><italic>Suggested citation for this article</italic>: Ogata T, Tanaka H. SARS-CoV-2 incubation period during Omicron BA.5&#x02013;dominant period, Japan. Emerg Infect Dis. 2024 Jan [<italic>date cited</italic>]. <ext-link xlink:href="https://doi.org/10.3201/eid3001.231487" ext-link-type="uri">https://doi.org/10.3201/eid3001.231487</ext-link></p></fn></fn-group><ref-list><title>References</title><ref id="R1"><label>1. </label><mixed-citation publication-type="journal"><string-name><surname>Cheng</surname>
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