[Changing management of pandemic influenza]

Abstract

In April 2009, for the first time in 41 years, a novel type of influenza A virus acquired the capacity for human-to-human transmission and caused a pandemic. This virus was derived from swine A (H1N1), which was a recombination of avian, human, and several swine influenza viruses, and named the "pandemic (H1N1) 2009 virus". As of mid-November, approximately 500,000 confirmed cases of pandemic (H1N1) 2009 infection had been reported to the World Health Organization. The true worldwide disease burden is yet unknown, but at least 100 times more people than those reported to the WHO have already been infected with this virus. The initial outbreak of this disease occurred in Mexico, and then the United States and Canada. Japan introduced strict quarantine measures including the screening of airline passengers for fever using thermography, which is useless for detecting patients during the incubation period. The result was that the first domestically-infected case was reported to be symptomatic on May 5th, four days prior to the detection of the first "imported cases" on May 9th at Narita Airport. This case was detected with other cases involved in a local outbreak of this disease through the strict policy of laboratory testing, i.e. focusing on cases that had any epidemiological link with known cases or overseas travel, which was implemented by the government. The epidemic seems to be close to its peak in Japan. The nature of the disease is mild, with mostly mild cases especially in younger generations. The case-fatality ratio is about 1:100,000 (0.001%), which is much lower than that of seasonal flu. A vaccination campaign is on the way, although vaccine supply is still very limited. In conclusion, there is still much uncertainty regarding this disease. The flexibility of the policy in response to its nature might have saved us from an initial catastrophe in affected regions, and should be well-reflected for the preparation of the next, unforeseeable pandemic of emerging infectious disease.