Seasonality and comparative dynamics of six childhood infections in pre-vaccination Copenhagen

Abstract

Seasonal variation in infection transmission is a key determinant of epidemic dynamics of acute infections. For measles, the best-understood strongly immunizing directly transmitted childhood infection, the perception is that term-time forcing is the main driver of seasonality in developed countries. The degree to which this holds true across other acute immunizing childhood infections is not clear. Here, we identify seasonal transmission patterns using a unique long-term dataset with weekly incidence of six infections including measles. Data on age -incidence allow us to quantify the mean age of infection. Results indicate correspondence between dips in transmission and school holidays for some infections, but there are puzzling discrepancies, despite close correspondence between average age of infection and age of schooling. Theoretical predictions of the relationship between amplitude of seasonality and basic reproductive rate of infections that should result from term-time forcing are also not upheld. We conclude that where yearly trajectories of susceptible numbers are perturbed, e.g. via waning of immunity, seasonality is unlikely to be entirely driven by term-time forcing. For the three bacterial infections, pertussis, scarlet fever and diphtheria, there is additionally a strong increase in transmission during the late summer before the end of school vacations.

Quantifying seasonal population fluxes driving rubella transmission dynamics using mobile phone data

“…For this analysis, we therefore fixed m at a consensus value of 0.97. Previous work (17) indicates that the exact value of m does not affect estimates of seasonal variation in transmission. We fit a different transmission parameter for every site in every month, to quantify how transmission varied throughout the year within each province, and then explored the degree to which the various proxies (including rainfall, school term times, and population flux quantified as above) performed as explanatory variables for fluctuations in transmission.…”

“…As a result, proxy measures such as school terms and rainfall patterns have been used (1,9,(13)(14)(15). Term time forcing, where school-driven aggregation leads to seasonal peaks of transmission for directly transmitted immunizing infections such as measles, mumps, and rubella, has been observed in many high-income countries (8,16,17) [England and Wales (8), Peru (15), and Denmark (17)]. On the other end of the spectrum in the low-income, predominantly agricultural context of Niger (13), analysis of night lights indicates that peaks in transmission reflect population changes resulting from annual mass migrations of individuals between agricultural areas to cities in the dry season (1).…”

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

“…Surprisingly, there remains much uncertainty regarding the drivers of seasonal incidence for numerous infections including polio, pertussis, scarlet fever, diphtheria, rotavirus, among others [5][6][7][8]. 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].…”

“…The ubiquity of seasonal variation in the incidence of infectious diseases has driven much epidemiological research focused on understanding the responsible underlying mechanisms [1][2][3][4][5]. Surprisingly, there remains much uncertainty regarding the drivers of seasonal incidence for numerous infections including polio, pertussis, scarlet fever, diphtheria, rotavirus, among others [5][6][7][8].…”

“…Surprisingly, there remains much uncertainty regarding the drivers of seasonal incidence for numerous infections including polio, pertussis, scarlet fever, diphtheria, rotavirus, among others [5][6][7][8]. 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].…”