Illustration of <a href="https://en.wikipedia.org/wiki/antigenic_shift" class="extiw" title="en:antigenic shift">antigenic shift</a>
<a href="https://en.wikipedia.org/wiki/National_Institute_of_Allergy_and_Infectious_Diseases" class="extiw" title="en:National Institute of Allergy and Infectious Diseases">National Institute of Allergy and Infectious Diseases</a> (NIAID)
2006
<a rel="nofollow" class="external text" href="http://www3.niaid.nih.gov/NR/rdonlyres/3D377A8B-747F-480A-832E-02A8ED9D1B3C/0/AntigenicShift_HiRes.jpg">National Institute of Health Website</a>