In March, 2009, a novel strain of swine-origin influenza-A H1N1 caused human infection in Mexico, and spread to all regions in the world in the following three months. On June 11, 2009, the World Health Organization declared that a global pandemic of influenza A H1N1 was underway. This action was a reflection of the spread of the new H1N1 virus, not the severity of illness caused by the virus. As of October, 2009, there are about 400,000 confirmed cases and 5000 mortalities due to pandemic H1N1 all over the world. The symptoms are usually mild: fever, cough, sore throat, muscle aches, and they usually disappear spontaneously within 3-7 days. Recommendations suggest staying at home with mild symptoms, and avoiding the contact with other people. In case of warning signs of complications or emergency symptoms, medical care is required, and antiviral treatment, hospitalization might be needed. The most important duty against pandemic H1N1 is prevention, which means first of all the adherence of hygienic rules and the use of vaccination. Based on epidemiologic data and worldwide experiences on influenza vaccination, both seasonal and H1N1 vaccinations are recommended for anyone 6 months of age or older who is at risk of becoming ill or of transmitting the viruses to others. Pregnant women during the first trimester are not recommended for vaccination, due to the lack of experiences. Overall, the rates and seriousness of a possible complication of influenza vaccination are much smaller than the risk of serious complications and mortality of influenza infection.