APA
World Health Organization, . (1990). International travel and health : vaccination requirements and health advice. World Health Organization, Geneva: .
Chicago
World Health Organization, . 1990. International travel and health : vaccination requirements and health advice. World Health Organization, Geneva: .
Harvard
World Health Organization, . (1990). International travel and health : vaccination requirements and health advice. World Health Organization, Geneva: .
MLA
World Health Organization, . International travel and health : vaccination requirements and health advice. World Health Organization, Geneva: . 1990.