by more original strains, that a variant showing considerable antigenic drift was identified in one isolate tested out of over 700. It ultimately came to be designated A/England/42/72. It was soon recognized, by comparison with the strains isolated then, that this virus had been the one responsible for the epidemic in India. The novel variant did not immediately spread after that outbreak, and circulating strains largely continued to resemble quite closely the original Hong Kong virus through April 1972. In May, however, at the onset of the flu season in the Southern Hemisphere, epidemics caused by the variant struck Malaysia, Singapore, and Australia, though South Africa and South America were unaffected. The die seemingly cast, the novel variant went on to cause widespread outbreaks in the Northern Hemisphere, by which point US press had dubbed the bug "London flu". It completely replaced the previous strains still resembling the original pandemic virus. In places such as the US and England and Wales, the 1972–1973 flu season was the deadliest since their respective deadliest waves of the pandemic between 1968 and 1970. Influenza A/H3N2 remains in circulation today as a strain of seasonal flu. Clinical data Flu symptoms typically lasted four to five days, but some cases persisted for up to two weeks. Virology The Hong Kong flu was the first known outbreak of the H3N2 strain, but there is serologic evidence of H3N1 infections in the late 19th century. The virus was isolated in Queen Mary Hospital. Soon after the initial outbreak in Hong Kong, the virus responsible was recognized to be antigenically distinct from the current influenza A strain in circulation (which at the time was called "A2") but was generally not considered an entirely new subtype. Analysis using the conventional techniques at the time revealed that it was indeed very different from older A2 viruses but also, at the same time, seemingly related to them, depending on one's reading of the data. Experiments involving newer methods of analysis soon identified another surface antigen, neuraminidase, in addition to hemagglutinin, which had already been recognized. It thus became clear that it was the hemagglutinin that had changed compared to older strains while the neuraminidase was identical. These findings, in part, prompted the World Health Organization in 1971 to revise its system of nomenclature for influenza viruses, taking into consideration both antigens. The novel virus was thereafter designated H3N2, indicating its partial