# Validating and Testing an Agent-Based Model for the Spread of COVID-19 in Ireland
## 2 Materials and Methods
### Model Description
#### 2.1.8 Interventions  
The above sections describe the agent movements and patterns when the model is not adapting its behaviors to a pandemic situation. This would be a likely scenario for the spread of an endemic disease such as influenza or measles where the population does not greatly adjust their behaviors during an outbreak. However, to better capture the response to the COVID-19 pandemic, the ability to simulate interventions and behavioral adaptations is important. Thus, we have included a number of interventions in the model. Lockdowns and School Closures  
Prior to the introduction of vaccinations, one of the main measures used to reduce the spread of the virus was change in behaviors. The fewer contacts individuals have, the less the virus will spread. In the model, the agents' behaviors are changed in two ways: schools are closed, or lockdowns are introduced. Primary and/or secondary schools can be closed: this requires all agents in the school to stay at home during school hours instead of attending school. A lockdown can be introduced that restricts agents' movements. During a lockdown, schools can be either opened or closed and the user can determine the percentage of agents who are working from home or no longer working as well as the reduction in movement around the community, compared to \"normal\" movements. Ireland implemented a comprehensive contact tracing program during the pandemic, where those who tested positive were contacted by contact tracers and their close contacts were identified and referred to a test [31]. The contact tracing program successfully completed contact tracing for 96% of the cases notified in Ireland between 17 March 2020 and 30 April 2021 [31]. However, due to the changing nature of the pandemic, the number of close contacts identified, the length of time to complete calls and the number of calls made varied throughout the pandemic. Additionally, not all contacts who were identified through contact tracing attended testing [32]. In the model, when an agent tests positive, a probability determines if they take part in contact tracing. This probability is estimated using the percent of cases in Ireland where contact tracing has been completed for a given month as a proxy. If the agent participates in contact tracing, then their contacts are identified, and a probability determines for each contact identified if that contact also participates in contact tracing. The probability is estimated using the percent of contacts that receive a test as a proxy. If an agent who is a contact of an infectious agent does participate in contact tracing, the agent isolates for a set number of days. In the first year of the pandemic, this isolation period was set to 14 days, as this was the suggested time to restrict movements when identified as a close contact. Contact tracing in the model can be turned on and off, and the parameters defining contact tracing (probability of a case participating, probability of a contact isolating and the number of days a contact isolates) can be adjusted to match what occurred at different times during the pandemic or to investigate potential scenarios. Vaccinations  
Vaccinations can also be turned on or off to investigate their impact on the pandemic. We include vaccinations in the model, but allow the user to turn vaccinations on and off. If vaccinations are turned on, then a vaccination spreadsheet is used as input to the model that provides information on the number of individuals by age group who have been vaccinated, who have successfully been protected against severe disease, who have successfully been protected against symptomatic disease and who have successfully been protected against asymptomatic disease. There are also different levels of protection against the two main variant, alpha and delta, that were circulating in Ireland in 2021. Thus an individual could be protected against asymptomatic disease from the alpha variant but only against symptomatic disease from the delta variant.