Final Report Summary - DECIDE (The impact of DEmographic Changes on Infectious DisEases transmission and control in middle/low income countries)
The aim of the DECIDE project was to evaluate the impact of demographic changes - such as fertility and mortality declines, urbanisation and changes in the household structure - on the spread of infectious diseases in low and middle income countries, and thus to allow a more realistic assessment of the effects of alternative control measures, in particular, immunisation activities, in resource-poor settings. To achieve these objective, the DECIDE team has: 1) gathered and analysed the available harmonised demographic and health survey datasets (DHS and HDSS) in order to parameterise mathematical models for infectious disease transmission in Sub-Saharan African countries; 2) conducted field studies in Kenya and Zimbabwe to collect data on social contact patterns and time use from representative samples of both urban and rural settings; 3) developed population dynamics and Agent-Based models (ABM) for the transmission of infectious disease to evaluate the impact of public health measures under changing demographic conditions.
Socio-demographic structures of these areas are extremely different from those of industrialized countries (i.e. younger age distribution, bigger family sizes, bigger class sizes at school) and these characteristics are found to strongly affect the level of social interactions that individuals have on a daily basis and, as a consequence, on the possible routes of infection transmission. Strong within-country heterogeneities showed us that in those areas where the degree of urbanization was higher and family structures were closer to the European context, also the level of interaction was much more resembling. These local characteristics should be taken into consideration when modelling infections in this settings and projecting future outcomes of intervention strategies.
The DECIDE project has generated realistic mathematical models for Respiratory Syncytial Virus (RSV), measles, Hepatitis B Virus (HBV), HIV, Ebola and Influenza. From all the analyses conducted, the effects of demographic processes, changing over time, as well as background demographic structures on infections spread and control is found to be substantial. In particular, we found that RSV household transmission is responsible for a very large proportion of infant infections and that school-age children are the main source of infection within the household, causing over half of the cases. Given these dependencies, annual vaccination of students is found to be the only alternative strategy to routine infants immunization and is able to trigger a relevant and persistent reduction of infant morbidity and mortality. The ABM model with background realistic and dynamic socio-demographic structures has been used to produce synthetic contact matrices for Kenya and to estimate the probability of an outbreak of Ebola Virus (EBV) in rural settings.
Through a deterministic compartmental model the impact of past and future changes in demographic processes and vaccination histories on measles epidemiology was evaluated for nine countries (both developed and developing). We found that there is the need to strengthen routine immunization efforts in developing countries to better cover younger age groups and to close the gap of susceptible adults especially in industrialized countries. Similarly, the impact of demographic changes on HBV epidemiology was assessed using data from the Gambia and from Senegal. In this analysis, we found that HBV underwent a substantial historical transition with demographic change as a major determinant. The onset of a demographically-driven decline in HBV prevalence, aligned with the expansion of HBV vaccination, forms a synergy that is potentially boosting the effectiveness of control strategies. Such a synergy is currently presenting a "window of opportunity" that can facilitate HBV elimination and that would be important to exploit.
All these results underline the importance of taking demographic structures and their changes over time into account when assessing the potential long-term impact of vaccine and other control measures.
Socio-demographic structures of these areas are extremely different from those of industrialized countries (i.e. younger age distribution, bigger family sizes, bigger class sizes at school) and these characteristics are found to strongly affect the level of social interactions that individuals have on a daily basis and, as a consequence, on the possible routes of infection transmission. Strong within-country heterogeneities showed us that in those areas where the degree of urbanization was higher and family structures were closer to the European context, also the level of interaction was much more resembling. These local characteristics should be taken into consideration when modelling infections in this settings and projecting future outcomes of intervention strategies.
The DECIDE project has generated realistic mathematical models for Respiratory Syncytial Virus (RSV), measles, Hepatitis B Virus (HBV), HIV, Ebola and Influenza. From all the analyses conducted, the effects of demographic processes, changing over time, as well as background demographic structures on infections spread and control is found to be substantial. In particular, we found that RSV household transmission is responsible for a very large proportion of infant infections and that school-age children are the main source of infection within the household, causing over half of the cases. Given these dependencies, annual vaccination of students is found to be the only alternative strategy to routine infants immunization and is able to trigger a relevant and persistent reduction of infant morbidity and mortality. The ABM model with background realistic and dynamic socio-demographic structures has been used to produce synthetic contact matrices for Kenya and to estimate the probability of an outbreak of Ebola Virus (EBV) in rural settings.
Through a deterministic compartmental model the impact of past and future changes in demographic processes and vaccination histories on measles epidemiology was evaluated for nine countries (both developed and developing). We found that there is the need to strengthen routine immunization efforts in developing countries to better cover younger age groups and to close the gap of susceptible adults especially in industrialized countries. Similarly, the impact of demographic changes on HBV epidemiology was assessed using data from the Gambia and from Senegal. In this analysis, we found that HBV underwent a substantial historical transition with demographic change as a major determinant. The onset of a demographically-driven decline in HBV prevalence, aligned with the expansion of HBV vaccination, forms a synergy that is potentially boosting the effectiveness of control strategies. Such a synergy is currently presenting a "window of opportunity" that can facilitate HBV elimination and that would be important to exploit.
All these results underline the importance of taking demographic structures and their changes over time into account when assessing the potential long-term impact of vaccine and other control measures.