Dynamics of the COVID-19 epidemic in Ireland under mitigation

Abstract Background: In Ireland and across the European Union, cases of COVID-19 continue to rise with recent increases in reported cases following a period of stability. Public health interventions continue in their attempts to control the epidemic in spite of a lack of information on the scale of silent transmission. Methods: To tackle this challenge and the non-stationary aspect of the epidemic we used a modified SEIR stochastic model with time-varying parameters, following Brownian process. This model is coupled with Bayesian inference (PMCMC) for parameter estimation and used mainly confirmed reported hospitalized cases. Results: Mitigation measures provided an 80% reduction in transmission between March and May 2020. By end of October our estimated seroprevalence rate was 1.1% (95% CI: 0.5%–2.8%) far from herd immunity. We estimated that the proportion of asymptomatic transmission was approximately 40% but with large uncertainty (95% CI: 14%–73%). Finally we demonstrate that the available observed confirmed cases are not reliable for any analysis owing to the fact that their reporting rate has greatly evolved. Conclusion: We provide the first estimations of the dynamics of the COVID-19 epidemic in Ireland and its key parameters. We also quantify the effects of mitigation measures on the virus transmission before, during and after mitigation. Our results demonstrate that Ireland has significantly reduced transmission by employing mitigation measures, physical distancing and lockdown. This has to date avoided the saturation of healthcare infrastructures, flattened the epidemic curve and likely reduced mortality. However, as mitigation measures change silent transmission remain an ongoing challenge.