National Influenza Centers

News. 2011-07-29 [2011-07-29]. （原始内容存档于2011-07-29）.  Influenza Type A Viruses and Subtypes. Centers for Disease Control and Prevention. 2013-04-02 [2013-06-13]

流感的盛行率在冬天達到高峰，由於北半球和南半球冬天的時間不同，因此事實上流感盛行的時間也不相同。這也是為何世界衛生組織（在國家流行性感冒中心（英语：National Influenza Centers）的協助下）每年對南北半球的疫苗配方有不同的建議。 流感為什麼總是季節性爆發而非全年都有一直是個未解之謎。一個可能的解釋是人

"Swine influenza A (H1N1) infection in two children --- Southern California, March--April 2009". Morbidity and Mortality Weekly Report. Centers for Disease

A, Lemon S. The Threat of Pandemic Influenza: Are We Ready? Workshop Summary (2005). Washington, D.C.: The National Academies Press. : 60–61 [2017-01-21]

pandemic...". U.S. Centers for Disease Control. Morbidity and Mortality Weekly Report Dispatch, April 21, 2009 （页面存档备份，存于互联网档案馆）. Influenza-Like Illness in