On the epidemiology of influenza

Abstract

The epidemiology of influenza swarms with incongruities, incongruities exhaustively detailed by the late British epidemiologist, Edgar Hope-Simpson. He was the first to propose a parsimonious theory explaining why influenza is, as Gregg said, "seemingly unmindful of traditional infectious disease behavioral patterns." Recent discoveries indicate vitamin D upregulates the endogenous antibiotics of innate immunity and suggest that the incongruities explored by Hope-Simpson may be secondary to the epidemiology of vitamin D deficiency. We identify -and attempt to explainnine influenza conundrums: (1) Why is influenza both seasonal and ubiquitous and where is the virus between epidemics? (2) Why are the epidemics so explosive? (3) Why do they end so abruptly? (4) What explains the frequent coincidental timing of epidemics in countries of similar latitude? (5) Why is the serial interval obscure? (6) Why is the secondary attack rate so low? (7) Why did epidemics in previous ages spread so rapidly, despite the lack of modern transport? (8) Why does experimental inoculation of seronegative humans fail to cause illness in all the volunteers? (9) Why has influenza mortality of the aged not declined as their vaccination rates increased? We review recent discoveries about vitamin D's effects on innate immunity, human studies attempting sick-to-well transmission, naturalistic reports of human transmission, studies of serial interval, secondary attack rates, and relevant animal studies. We hypothesize that two factors explain the nine conundrums: vitamin D's seasonal and population effects on innate immunity, and the presence of a subpopulation of "good infectors." If true, our revision of Edgar Hope-Simpson's theory has profound implications for the prevention of influenza.

The Effect of Vitamin D Deficiency on the Severity of Bronchiolitis in Infants

“…Many studies have proposed that vitamin D concentration decreases due to the decrease in sunlight during the winter months, resulting in a related decrease in immune functions and sensitivity to influenza infections (12,13).…”

Human skin pigmentation, migration and disease susceptibility

“…Low vitamin D levels have been connected to epidemics of influenza [63]. Vitamin D plays an important part in cancer prevention [40,64], but the results of controlled clinical trials are needed to establish the extent of its protective action relative to, or in addition to, genetically based risk.…”

Human birth seasonality: latitudinal gradient and interplay with childhood disease dynamics

“…Early work on diphtheria and measles implicated elevated contact rates among children in school as the driver of pulsed transmission [1,9], leading to much emphasis on school-term forcing [2,3,5,10,11]. More recently, additional mechanisms of seasonal transmission have been identified, including climatic drivers of pathogen survival [12], transmission [13,14] and vector activity [15,16], seasonal host migration [17] and seasonal fluctuations in host immunity [18,19]. Here, we propose that seasonality in host recruitment rates may also shape epidemiology.…”