Светска здравствена организација — разлика између измена

* {{Cite book | ref = harv | last1 = Orenstein| first = Walter A. | last2 = Plotkin| first2 = Stanley A. | title = Vaccines | url = https://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=smallpox&rid=vacc.section.45#47| publisher=W.B. Saunders Co| location = Philadelphia | year = 1999| isbn = 978-0-7216-7443-8| pages = }}

* {{Cite book | ref = harv | last = Fenner| first = Frank | title = Smallpox and Its Eradication | series = History of International Public Health | volume = 6 | publisher = World Health Organization | location = Geneva| year = 1988| chapter = Development of the Global Smallpox Eradication Programme | chapterurl = https://biotech.law.lsu.edu/blaw/bt/smallpox/who/red-book/9241561106_chp9.pdfhttps://biotech.law.lsu.edu/blaw/bt/smallpox/who/red-book/9241561106_chp9.pdf | isbn = 978-92-4-156110-5| pages = 366–418}}