Other competing hypotheses include differences in preexisting population immunity or socioeconomic factors, but these are less parsimonious explanations.
Population immunity likely is an important factor of epidemic occurrence and heterogeneous vaccination coverage across the district may explain why some outbreaks remain localised and why outbreaks may occur several years in a row despite vaccination campaigns.
Non-climatic factors like vector abundance, population immunity, etc., have been studied as influential factors for malaria incidence [25] and Hay et al. [26] predicted malaria seasonal pattern in Kenya using Normalized Difference Vegetation Index (NDVI).
The reason our study found a higher rate of infection in household contacts of shigellosis patients is unknown but may reflect differences in environmental risk factors or population immunity.
Biologic, ecologic, and social factors such as population immunity level, abundance and infection rate of host rodents, and human behavior, also may affect transmission of HFRS.
The remaining 31-67% of the variation possibly involved non-climatic causes, such as population immunity [ 16- 19] and socio-environmental factors that influence the breeding and ecology of mosquito vectors [ 20- 23].
Extrinsic factors, including climatic and environmental variables, have been hypothesized to drive annual seasonality; intrinsic factors associated with human host demographics, population immunity, and the virus, drive the multiannual dynamics (5 – 7 ).
There are likely to be multiple, poorly understood interactions between climatic, environmental and behavioural factors, and complex interplay between different circulating viruses and population immunity.
Second, little biological or behavioral information was available on community- or individual-level factors (e.g., mosquito population densities, human behaviors, and population immunity) that may potentially confound associations between the socioecological characteristics examined and DF transmission.
