Role of children in the Bulgarian COVID-19 epidemic: A mathematical model study

Figure 1 Relative growth of cases by age groups. An apparent lag between 0-19 and others can be seen.

Figure 2 Sample cross-correlation function between new weekly cases of coronavirus disease 2019 and multisystem inflammation in children cases. MIS-C: Multisystem inflammation in children.

Figure 3 Relative growth of national-level coronavirus disease 2019 cases and multisystem inflammation in children cases in Pirogov Hospital. COVID-19: Coronavirus disease 2019; MIS-C: Multisystem inflammation in children.

Figure 4 Principal component analysis Biplot for age groups on a weekly basis. PCA: Principal component analysis.

Figure 5 Residuals of Model I – Factors contributing to the spread among children. A: Residuals of the model; B: Autocorrelation function of the residuals; C: Distribution of the residuals.

Figure 6 Fitted Model I – Factors contributing to the spread among children. COVID-19: Coronavirus disease 2019.

Figure 7 Residuals of MODEL III –III – Temporal spread across age groups 20-49. A: Residuals of the model; B: Autocorrelation function of the residuals; C: Distribution of the residuals.

Figure 8 Fitted MODEL III – Temporal spread across age groups 20-49. COVID-19: Coronavirus disease 2019.

Figure 9 Residuals of Model II – Temporal spread across age groups 60-89. A: Residuals of the model; B: Autocorrelation function of the residuals; C: Distribution of the residuals.

Figure 10  Fitted Model II – Temporal spread across age groups 60-89. COVID-19: Coronavirus disease 2019.

Figure 11  Probability density distribution of the number of multisystem inflammation in children cases on a weekly basis. Poisson distribution for total cases up to 4.12.2021 is with λ = 0.50∈ [0.355, 0.835]. MIS-C: Multisystem inflammation in children.

Figure 12  Residuals of model for the bi-weekly period. A: Residuals of the model; B: Autocorrelation function of the residuals; C: Distribution of the residuals.

Figure 13  Fitted model for a bi-weekly period. MIS-C: Multisystem inflammation in children.

Figure 14  Share of fully vaccinated individuals per age group up to November 16, 2021. Data for the number of fully vaccinated individuals is taken from[35].