The pH1N1 virus rapidly traveled around the world. As of June 9, 2009, a total of 73 countries had reported more than 26,000 laboratory-confirmed cases, and the World Health Organization (WHO) declared that the situation met the criteria for a phase 6 pandemic. By the time the pandemic had waned in August 2010, virtually all countries had reported laboratory-confirmed cases. While exact figures of the death toll from pH1N1 are unknown, estimates range from 105,700 to 395,600 deaths. The WHO provided early recommendations on administering vaccine to target groups and valuable field assistance to affected countries. WHO efficiently distributed more than 3 million courses of antiviral drugs to 72 countries. Surveillance and epidemiologic investigations are critical public health functions during outbreaks, epidemics and pandemics. Thus, timely public health surveillance and epidemiologic investigations are crucial for an effective public health response because they allow public health officials to gather health information, prioritize response activities, and make appropriate public health decisions. Global influenza surveillance has been conducted through the WHO Global Influenza Surveillance and Response System (GISRS) since 1952. The current network is comprised of six WHO collaborating centers, four essential regulatory laboratories and 136 institutions in 106 WHO member states, which are recognized by WHO as national influenza centers.