Presentation on theme: "Transmission effect of contact redistribution Reducing the contacts among children leads to more contacts with adults due to supervision. Using a data-based."— Presentation transcript:
Transmission effect of contact redistribution Reducing the contacts among children leads to more contacts with adults due to supervision. Using a data-based contact matrix (AmJEpidemiol 2006;164:936) and German demographic data, we examine the joined effect of reducing child-child Should schools be closed during an influenza pandemic? M. Eichner 1, C. Winter 2,3, S.O. Brockmann 3, G. Pfaff 3, H.P. Duerr 1, M. Schwehm 1 1 Department of Medical Biometry, University of Tübingen, Germany 2 Robert Koch Institute, Berlin, Germany 3 Baden-Württemberg State Health Office, Stuttgart, Germany Closing of day care centers and schools, and canceling of mass gathering events have been used to mitigate epidemics of seasonal influenza and other infectious diseases. This strategy is currently being discussed in the context of pandemic influenza. For seasonal influenza, children represent a sig- nificant proportion of the suscep- tible population, but this will not hold for a new pandemic strain. We use mathematical modeling to exa- mine the influnce of such interven- tions in a pandemic situation where pre-existing immunity in the popu- lation does no exist. School (closing): assumptions Children have about 40% of their contacts with other children of the same age. We assume that 75% of these contacts occur in schools or day care centres and can be pre- vented. Severely ill children stay at home and thus, have no school contacts. Instead they have twice as many contacts with nursing adults, com- pared to healthy children of the same age. While schools and day care cen- ters are closed, the contacts a- mong healthy children are reduced to the same extent. Their contacts with adults increase by 50% due to supervision at home. General model features Model type: deterministic model. R 0 =2.5. Demography: Age-structured po- pulation of Germany with data- based age-mixing matrix; popula- tion size 100,000. Natural history of disease as illus- trated above. Additional interventions: 10% general contact reduction, partial isolation of cases (leading to con- tact reduction of 10-30%), antiviral treatment of all severe cases. It has been claimed that "school closure during the peak of a pandemic can reduce peak attack rates by up to 40%, but has little impact on overall attack rates" (Nature 2006;442:448). This cannot be confirmed in our studies where a slight beneficial effect of school closure can only be produced if very few of the prevented contacts are redirected to adults. If school closure causes children to have at least 30% more contacts with adults, transmission even increases, leading to a quicker spread and to higher numbers of cases. BackgroundNatural History of DiseaseUser Interface ResultsMethods Open Source Project Conclusions InfluSim is an open source project. The source code can be downloa- ded from influsim.sourceforge.net. More information is available under and feature requests are welcome. Susceptible At home (untreated) Very sick Moderately sick Asymp- tomatic Hospitalized (untreated) Infected Extremely sick age risk age At home (treated) age Hospitalized (treated) age Immune and recovered Dead age doctoral visit Immune and convalescent age Effect of school closing on a pandemic wave Using the freely available program InfluSim (ver- sion 2.0), we study how closing day care centers and schools for one month affects the course of a pandemic wave (see Methods for parameter val- ues). In the absence of adult immunity, school clo- sure increases transmission, leading to a peak which can occur up to 3 days earlier and can be considerably higher, especially if it starts soon af- ter introduction of the infection; e. g., the peak number of hospital beds needed by influenza pa- Transmission increased Transmission reduced 0%50%100% Contacts in school or day care center 0% 50% 100% Additional contacts with adults based on InfluSim 2.0 1/3 As this effect does not occur for seasonal influ- enza, we have also looked at adult immunity: the described increase in transmission disappears if at least 30% of adults are immune. contacts and incre- asing child-adult contacts. Even if all contacts among children can be prevented, trans- mission increases if their contacts with adults increa- se by 30%. tients increases from 43 to up to 50 in a popula- tion of 100,000 in- habitants and the cumulative num- ber of influenza patients increases by more than 5%. Assuming that severely ill cases stay at home for 12 days, 15-25% of working adults (depending on the effectiveness of interventions) cannot go to work at the peak of the epidemic because they are sick. A further fraction of the working population will probably stay at home to take care of sick relatives. School closing may not only increase transmission, but will further increase the number of adults who have to stay at home to take care of their children. The combined work loss may well jeopardize hospitals and other crucial services.