Purpose: To evaluate the impact of mass changes in social mixing patterns such as holiday traveling, public gatherings, or visiting medical providers on the course of an influenza pandemic in order to aid decision making on (i) whether to postpone/cancel mass gatherings or (ii) whether to open physically separate clinics for influenza treatment.
Method: We develop an agent-based model of influenza transmissions with daily social mixing through households, work or school groups, community locations, and temporary gathering sites that represent settings including mass gatherings, holiday travelling, and patients visiting hospitals/clinics with influenza-like-illness (ILI) symptoms. Using demographic data from the state of Georgia, we run experiments with different combinations of the length of the mass gathering or traveling period, the proportion of the population with changes in social mixing, the timing of providing clinics for persons with ILI and the likelihood of visiting hospitals/influenza clinics, and the reproductive number R0.
Result: Holiday traveling can lead to a second epidemic peak under certain scenarios. Mass gatherings that occur within 10 days before the epidemic peak can result in as high as 10% increases in the state-wide peak prevalence level and total attack rate, while both measures are 3-5% higher among the attendees and their family members than others. Persons with ILI visiting hospitals may contribute to a 5-10% higher peak prevalence level by exposing uninfected persons concomitantly seeking care in hospitals. Opening physically separate influenza clinics to manage persons with ILI can result in reduction of the peak prevalence level of 15% (when open throughout epidemic) or 12% (when open 40 days before and after the epidemic peak), even when patients are more likely to visit clinics than hospitals; both cases reduced hospital-acquired infections by 45%.
Conclusion: Our results show that pandemic response should not necessarily be slowed even after a large decline in influenza activity if social mixing patterns have been changing. Temporal learning suggests that postponing or cancelling large public gatherings may significantly reduce transmission of pandemic infections when occurring close to the epidemic peak but not much when occurring more than 1 month from the peak time. Creation of physically separate ILI management clinics effectively reduces influenza transmission occurring in the hospital setting and the prevalence level even if not open all days.
Candidate for the Lee B. Lusted Student Prize Competition