How Flu Spreads | Influenza (Flu)

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Higher Risk </a> <a data-post-id="133542" href="/flu/prevention/index.html" tabindex="0"> Prevention </a> <a data-post-id="133754" href="/flu/vaccines/index.html" tabindex="0"> Vaccine Basics </a> <a data-post-id="133752" href="/flu/testing/index.html" tabindex="0"> Diagnosis </a> <a data-post-id="133541" href="/flu/treatment/index.html" tabindex="0"> Flu Treatment </a> <a class="view-all" href="/flu/site.html"> View All </a> </div> </div> </header> <main class="container cdc-main" role="main" aria-label="Main Content Area"> <section class="cdc-page-title-bar cdc-page-offset noindex"> <time class="cdc-page-title-bar__item cdc-page-title-bar__item--date" datetime="2024-09-17 04:00:00"> September 17, 2024 </time> <div data-alt-langs class="cdc-page-title-bar__item cdc-page-title-bar__item--languages"> <a class="cdc-page-title-bar__item" href="https://espanol.cdc.gov/enes/flu/spread/index.html">Español</a> </div> </section> <div class="cdc-page-title cdc-page-offset syndicate"> <h1>How Flu Spreads</h1> </div> <div id="content" class="cdc-page-content cdc-page-offset syndicate container"> <div class="cdc-dfe-body "> <div class="cdc-dfe-body__top "> <div class="dfe-section dfe-section--page-summary summary-list" data-section="cdc_causes_page_summary"> <div class="dfe-section__header"> <h2 class="editor-block--title" id="heading-_gv3knmf1w">What to know</h2> </div> <div class="dfe-section__content"> <ul class="nested-list"> <li class="level-1">Experts think that influenza viruses spread mainly by droplets made when people with flu cough, sneeze, or talk.<ul> </ul> </li> <li class="level-1">Less often, a person might get influenza (flu) by touching a surface or object that has influenza virus on it and then touching their own mouth, nose, or possibly their eyes.<ul> </ul> </li> <li class="level-1">Influenza viruses can be detected in most infected people beginning one day before symptoms develop and up to five to seven days after becoming sick.<ul> </ul> </li> <li class="level-1">People with flu are the most contagious during the first three days of their illness<ul> </ul> </li> </ul> <div class="dfe-section__nav hide" id="dfe-section__nav"> <div class="dfe-section__nav__header" id="dfe-section__nav__header"> </div> <div class="dfe-section__nav-links" id="dfe-section__nav-links"> </div> </div> </div> <div id="nav-buttons"> </div> </div> </div> <div class="cdc-dfe-body__center "> <div class="dfe-section" data-section="cdc_causes_why_it"> <a class="onThisPageAnchor" id="cdc_causes_why_it-why-it-spreads" name="Why%20it%20spreads" title="Why it spreads"></a><h2 class="editor-block--title" id="heading-eeopmsgakt">Why it spreads</h2> <p>People with flu can spread it to others. Most experts think that influenza viruses spread mainly by droplets made when people with flu cough, sneeze, or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Putting <a href="https://www.cdc.gov/respiratory-viruses/prevention/physical-distancing.html">physical distance</a> between yourself and others can help lower the risk of spreading a respiratory virus. Less often, a person might get flu by touching a surface or object that has influenza virus on it and then touching their own mouth, nose, or possibly their eyes.</p> </div> <div class="dfe-section" data-section="cdc_causes_myth"> <a class="onThisPageAnchor" id="cdc_causes_myth-when-are-people-with-flu-contagious" name="When%20Are%20People%20with%20Flu%20Contagious?" title="When Are People with Flu Contagious?"></a><h2 class="editor-block--title" id="heading-ztugnsz7ai">When Are People with Flu Contagious?</h2> <p>Influenza viruses can be detected in most infected persons beginning one day <strong>before </strong>symptoms develop and up to five to seven days <strong>after </strong>becoming sick. People with flu are most contagious during the first three days of their illness. Some people, including young children and people with weakened immune systems may be contagious for longer periods of time. </p> <p>Symptoms typically begin about two days (but can range from one to four days) after influenza viruses infect a person's respiratory tract. It is theoretically possible that before symptoms begin, an infected person can spread influenza viruses to their close contacts. 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