Impact of Birth Seasonality on Dynamics of Acute Immunizing Infections in Sub-Saharan Africa

Abstract

We analyze the impact of birth seasonality (seasonal oscillations in the birth rate) on the dynamics of acute, immunizing childhood infectious diseases. Previous research has explored the effect of human birth seasonality on infectious disease dynamics using parameters appropriate for the developed world. We build on this work by including in our analysis an extended range of baseline birth rates and amplitudes, which correspond to developing world settings. Additionally, our analysis accounts for seasonal forcing both in births and contact rates. We focus in particular on the dynamics of measles. In the absence of seasonal transmission rates or stochastic forcing, for typical measles epidemiological parameters, birth seasonality induces either annual or biennial epidemics. Changes in the magnitude of the birth fluctuations (birth amplitude) can induce significant changes in the size of the epidemic peaks, but have little impact on timing of disease epidemics within the year. In contrast, changes to the birth seasonality phase (location of the peak in birth amplitude within the year) significantly influence the timing of the epidemics. In the presence of seasonality in contact rates, at relatively low birth rates (20 per 1000), birth amplitude has little impact on the dynamics but does have an impact on the magnitude and timing of the epidemics. However, as the mean birth rate increases, both birth amplitude and phase play an important role in driving the dynamics of the epidemic. There are stronger effects at higher birth rates.

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

“…As has been found in high-income settings, but in contrast to other African countries, rubella transmission was strongly positively related to school term times (t test, t = −3.6681, df = 80.505, P < 1e-3 for provinces excluding the Northeastern province where power for analysis was weak); transmission was not significantly correlated with rainfall (mean correlation coefficient, −0.13; 95% quantile interval, −0.34, 0.07, P > 0.2, excluding the Northeastern province; Fig. S3 and Table S1) (1,13,27,28). There was also a strong positive relationship with province-level population flux in the previous month normalized for each province (mean correlation coefficient, 0.38; 95% quantile interval, 0.18, 0.55, P < 1e-3, excluding the Northeastern province).…”

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

“…In these settings, our findings have the potential to explain some of the spatial and temporal variation observed in the periodicity of diseases such as measles, rotavirus and polio; and present a promising avenue for future research. Indeed, a recent study of birth seasonality across developing countries found that the timing of the birth peak influences epidemic timing, and a high birth rate magnifies the effect of birth seasonality on measles epidemics [59]. Although our study-focused exclusively on measles epidemiologysuggests that high amplitude birth seasonality is required to alter disease incidence, we predict that lower birth amplitudes may have a dynamical effect when coupled with a higher mean birth rate or for childhood diseases with longer infectious periods that may exhibit less frequency-locking with seasonal transmission [7].…”

Measuring fertility through mobile‒phone based household surveys: Methods, data quality, and lessons learned from PMA2020 surveys

“…The redistribution assumes that not knowing the month of the birth is unassociated with the actual birth month. Considering seasonality in birth (Dorélien 2016;Dorélien, Ballesteros, and Grenfell 2013), a redistribution proportional to reported birth month can introduce another bias, depending on the month in which the two-year reference period starts, as explained further below. Table 5 shows the total number of births falling in the two-year reference period after the adjustment.…”