subtype of influenza A, only a variant of older strains. Nevertheless, the World Health Organization warned of potential worldwide spread of the virus on 16 August. An outbreak of influenza-like illness in Singapore during the second week of August was the first indication of spread outside of Hong Kong. Around the same time, an outbreak became apparent in the Philippines and Malaysia, and, before the end of the month, an epidemic was underway in the Republic of Vietnam. The first known cases of the flu in the United Kingdom were identified in early August in an infant and her mother in London with no history of travel or known contact with anyone with a history of travel from the Far East. More isolated cases soon followed, but it was not until September that larger outbreaks began occurring in school settings. In September 1968, the flu reached India, northern Australia, Thailand, and Europe. The same month, the virus entered the United States and was carried by troops returning from the Vietnam War, but it did not become widespread in the country until December 1968. During the second week of September, nearly 2000 participants from 92 countries, including some in southeast Asia where the flu was epidemic, met in Tehran for the Eighth International Congresses on Tropical Medicine and Malaria. An outbreak of influenza soon erupted among the participants, afflicting at least a third of them. The convention was the apparent origin of a broader outbreak within the capital city, which thereafter spread rapidly throughout Iran. The virus entered Japan repeatedly throughout August and September, but these introductions did not spark any larger outbreak. The first "true epidemic" began in early October, almost entirely confined to school settings. In the USSR, the first cases of the flu began to appear in mid-December. It reached Africa and South America by 1969. The development of the pandemic at first resembled that of the 1957 pandemic, which had spread unencumbered throughout the spring and summer and had become truly worldwide by October, by which point nearly all countries were experiencing their first or even second wave. However, the two experiences eventually diverged within a couple of months after their initial outbreaks. In 1968, many countries (e.g., the UK, Japan) did not immediately see outbreaks despite repeated introductions of the virus throughout August and September. Additionally, after September, there was little evidence of continued spread in