{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,15]],"date-time":"2026-10-15T12:48:24Z","timestamp":1792068504067,"version":"4.4.0"},"reference-count":31,"publisher":"American Medical Association (AMA)","issue":"4","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JAMA Netw Open"],"abstract":"<jats:sec id=\"ab-zoi250290-4\"><jats:title>Importance<\/jats:title><jats:p>Multiple studies have identified an association between COVID-19 vaccination and menstrual disturbances. Data on whether menstrual health is impacted by other vaccines are needed to counsel individuals about what to expect and to address vaccine hesitancy.<\/jats:p><\/jats:sec><jats:sec id=\"ab-zoi250290-5\"><jats:title>Objective<\/jats:title><jats:p>To assess the association of changes in length of the menstrual cycle with influenza vaccination, with or without concurrent receipt of a COVID-19 vaccine.<\/jats:p><\/jats:sec><jats:sec id=\"ab-zoi250290-6\"><jats:title>Design, Setting, and Participants<\/jats:title><jats:p>This global retrospective cohort study prospectively collected menstrual cycle data from April 25, 2023, to February 27, 2024 (4-5 cycles per individual), among international English-speaking users of a digital birth control application. Participants included individuals aged 18 to 45 years, not using hormonal contraception, and with average cycle lengths of 24 to 38 days in 3 consecutive cycles before receipt of vaccines.<\/jats:p><\/jats:sec><jats:sec id=\"ab-zoi250290-7\"><jats:title>Exposure<\/jats:title><jats:p>Seasonal influenza vaccination with or without concurrent receipt of COVID-19 vaccine.<\/jats:p><\/jats:sec><jats:sec id=\"ab-zoi250290-8\"><jats:title>Main Outcome and Measure<\/jats:title><jats:p>The primary outcome consisted of adjusted mean within-individual changes of menstrual cycle length assessed by vaccination group. Secondary analysis evaluated the phase of menstrual cycle at time of vaccination.<\/jats:p><\/jats:sec><jats:sec id=\"ab-zoi250290-9\"><jats:title>Results<\/jats:title><jats:p>A total of 1501 individuals met the inclusion criteria, of whom 791 were vaccinated for influenza only and 710 were concurrently vaccinated for influenza and COVID-19. By race and ethnicity, 1 participant (0.1%) was American Indian or Alaska Native; 10 (0.7%), Asian; 3 (0.2%), Black; 15 (1.0%), Hispanic or Latina; 1 (0.1%), Middle Eastern or North African; 368 (24.5%), White; and 19 (1.3%), other; and 1084 (72.2%), missing. Most of the cohort was younger than 35 years (1230 [82.0%]), had at least a college degree (1122 [74.8%]), and was located in the US or Canada (938 [62.5%]). Individuals vaccinated for influenza alone experienced an adjusted mean increase of 0.40 (95% CI, 0.08-0.72) days, while those vaccinated concurrently for influenza and COVID-19 experienced a mean increase of 0.49 (95% CI, 0.16-0.83) days (<jats:italic>P<\/jats:italic>\u2009=\u2009.69 for difference between vaccine groups). A total of 37 individuals (4.7%) experienced a change in cycle length of at least 8 days with influenza vaccine only and 42 (5.9%) with concurrent receipt of both vaccines (<jats:italic>P<\/jats:italic>\u2009=\u2009.28). In the postvaccination cycle, both vaccination groups returned to their prevaccination cycle lengths. Menstrual cycle changes occurred with vaccination in the follicular phase but not the luteal phase.<\/jats:p><\/jats:sec><jats:sec id=\"ab-zoi250290-10\"><jats:title>Conclusions and Relevance<\/jats:title><jats:p>In this cohort study of individuals with regular menstrual cycles, influenza vaccine given alone or in combination with a COVID-19 vaccine was associated with a small but temporary change in menstrual cycle length. These findings may help clinicians confirm the utility of vaccination for patients with concerns about menstrual adverse effects of vaccination.<\/jats:p><\/jats:sec>","DOI":"10.1001\/jamanetworkopen.2025.7871","type":"journal-article","created":{"date-parts":[[2025,4,29]],"date-time":"2025-04-29T15:31:25Z","timestamp":1745940685000},"page":"e257871","source":"Crossref","is-referenced-by-count":2,"title":["Menstrual Cycle Length Changes Following Vaccination Against Influenza Alone or With COVID-19"],"prefix":"10.1001","volume":"8","author":[{"given":"Emily R.","family":"Boniface","sequence":"first","affiliation":[{"name":"Department of Obstetrics and Gynecology, Oregon Health & Science University, Portland"},{"name":"OHSU-PSU (Oregon Health & Science University\u2013Portland State University) School of Public Health, Portland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Blair G.","family":"Darney","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynecology, Oregon Health & Science University, Portland"},{"name":"OHSU-PSU (Oregon Health & Science University\u2013Portland State University) School of Public Health, Portland"},{"name":"Instituto Nacional de Salud P\u00fablica, Centro de Investigaci\u00f3n en Salud Poblacional, Cuernavaca, M\u00e9xico"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Agathe","family":"van Lamsweerde","sequence":"additional","affiliation":[{"name":"Natural Cycles Nordic AB, Stockholm, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Eleonora","family":"Benhar","sequence":"additional","affiliation":[{"name":"Natural Cycles Nordic AB, Stockholm, Sweden"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alexandra","family":"Alvergne","sequence":"additional","affiliation":[{"name":"Institut des Sciences de l\u2019Evolution de Montpellier, Montpellier University, Centre National de la Recherche Scienti\ufb01que, Institut de Recherche pour 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