The importance of vaccine on public health is related to the herd protection related to the levels of vaccine coverage, which directly influences the vaccinated individuals as well as the unvaccinated community. Reaching the level of herd protection by increasing vaccine coverage is the basic strategy to eradicate related infectious diseases. Again, herd protection has played an important role in public health practices. With the increasing interests in estimating the vaccine herd protection, we however, have seen only few relevant papers including observational population-based and cluster-randomized clinical trials reported in China. We hope to discuss the study designs for evaluating the vaccine herd protection in order to generate evidence-based related research in this field.
China/epidemiology* ; Communicable Disease Control ; Communicable Diseases/immunology* ; Humans ; Immunity, Herd/immunology* ; Research Design ; Vaccination/trends* ; Vaccines/immunology*

INTRODUCTIONWe investigated the 2005 outbreak of dengue fever (DF)/dengue haemorrhagic fever (DHF) to determine its epidemiological, virological and entomological features to further understand the unprecedented resurgence.

MATERIALS AND METHODSAll physician-diagnosed, laboratory-confirmed cases of DF/DHF notified to the Ministry of Health, Singapore during the outbreak as well as entomological and virological data were analysed retrospectively.

RESULTSA total of 14,006 cases of DF/DHF comprising 13,625 cases of DF and 381 cases of DHF, including 27 deaths were reported, giving an incidence rate of 322.6 per 100,000 and a case-fatality rate of 0.19%. The median age of the cases and deaths were 32 and 59.5 years, respectively. The incidence rate of those living in compound houses was more than twice that of residents living in public and private apartments. The distribution of DF/DHF cases was more closely associated with Aedes aegypti compared to Aedes albopictus breeding sites and the overall Aedes premises index was 1.15% (2.28% in compound houses and 0.33% to 0.8% in public and private apartments). The predominant dengue serotype was DEN-1. A significant correlation between weekly mean temperature and cases was noted. The correlation was strongest when the increase in temperature preceded rise in cases by a period of 18 weeks.

CONCLUSIONThe resurgence occurred in a highly densely populated city-state in the presence of low Aedes mosquito population. Factors contributing to this resurgence included lower herd immunity and change in dominant dengue serotype from DEN-2 to DEN-1. There was no evidence from gene sequencing of the dengue viruses that the epidemic was precipitated by the introduction of a new virulent strain. The current epidemiological situation is highly conducive to periodic dengue recurrences. A high degree of vigilance and active community participation in source reduction should be maintained.

Adult ; Aedes ; Animals ; Dengue ; epidemiology ; prevention & control ; transmission ; Dengue Virus ; immunology ; isolation & purification ; pathogenicity ; Disease Outbreaks ; Female ; Humans ; Immunity, Herd ; Incidence ; Insect Vectors ; Male ; Middle Aged ; Mosquito Control ; Primary Prevention ; methods ; Public Health ; Retrospective Studies ; Risk Factors ; Serotyping ; Singapore ; epidemiology