Seven historical datasets of smallpox were reanalyzed to examine the presence of seasonality and to identify the characteristic factors. Annual cycles were clearly shown not only in the monthly reports but also in the estimates of the effective reproduction number. Even for a short-term epidemic, the transmission of smallpox would most likely be enhanced by dry weather. Chinese journals: a guide for epidemiologists Chinese journals in epidemiology, preventive medicine and public health contain much that is of potential international interest. However, few non-Chinese speakers are acquainted with this literature. This article therefore provides an overview of the contemporary scene in Chinese biomedical journal publication, Chinese bibliographic databases and Chinese journals in epidemiology, preventive medicine and public health. The challenge of switching to English as the medium of publication, the development of publishing bibliometric data from Chinese databases, the prospect of an Open Access publication model in China, the issue of language bias in literature reviews and the quality of Chinese journals are discussed. Epidemiologists are encouraged to search the Chinese bibliographic databases for Chinese journal articles. The Chinese have had a long history in infectious disease control, and records of epidemics can be traced back two millennia [1] . Since the introduction of modern medicine by missionary doctors in the 19 th century [2] , modern epidemiological studies have been conducted in China, first by Western doctors, and then gradually superseded by their Chinese colleagues in the 1930s [3] . Since the 1950s, huge reductions in the incidence of infectious diseases like measles and schistosomiasis have been achieved through national vaccination programmes and environmental intervention programmes [1, 4] . The adoption of the Open Door Policy in 1978 marked the beginning of remarkable social and economic development unprecedented in China's modern history. However, rapid industrialization and urbanization are accompanied by many social problems, from the increasing rich-poor, urban-rural, coastal-interior disparity to heavy environmental pollution. Changes in disease profile with the increasing burden of non-communicable diseases as a result of an aging population with a successful one-child policy posed new challenges in the 21 st century [1] . The SARS epidemic in 2003 exposed how a lack of transparency and delayed dissemination of information on the part of the Chinese government made an epidemic of then unknown aetiology a global problem [3] .