Impact of Superspreaders on dissemination and mitigation of COVID-19

Abstract Background The draconian measures used to control COVID-19 dissemination have been highly effective but only at enormous socioeconomic cost. Evidence suggests that “superspreaders” who transmit the virus to a large number of people, play a substantial role in transmission; recent estimates suggest that about 1-20% of people with the virus are the source for about 80% of infections. We used an agent-based model to explore the interplay between social structure, mitigation and superspreading. Methods We developed an agent-based model with a subset of “superspreader” agents that transmit disease far more efficiently. These agents act in a social network that allows transmission during contacts in three sectors: “home,” “work/school” and “other”. We simulated the effect of various mitigation strategies that limit contacts in each of these sectors, and used the model to fit COVID-19 mortality data from Sweden. Findings Reducing contacts in the “other” sector had a far greater impact on epidemic trajectory than did reducing “home” or “work/school” contacts; this effect was substantially enhanced when the infectivity of children was reduced relative to that of adults. The model fit Swedish hospitalization data with reasonable assumptions about the effect of Sweden’s mitigation policies on contacts in the different sectors. Interpretation Our results suggest COVID-19 could be controlled by limiting large gatherings and other opportunities for contacts between people in restaurants, sporting events, concerts and worship services) while still allowing regular contacts in the home or at work and school. Research in context Evidence before this study Superspreading events have long been known to be important in the epidemiology of many infectious diseases, including tuberculosis, measles, Ebola and SARS. Since the emergence of SARS-CoV-2, epidemiologic analyses have inferred substantial individual-level variation in transmissibility, with an estimated 1% to 20% of infected persons causing about 80% of all COVID-19 cases. Added value of this study We developed an agent-based socially structured model to simulate the effect of superspreaders in COVID-19 transmission in the context of country-wide “lockdown” policies. These simulations indicate that COVID-19 can be effectively mitigated by limiting contacts between people who otherwise rarely meet, while allowing home and most work/school contacts to continue. Implications of all available evidence It is crucial to include heterogeneity in individual infectiousness when modeling the impact of mitigation strategies on observed COVID-19 epidemic patterns. Reducing opportunities for superspreading by limiting random contacts outside home and work could be the most effective way to control COVID-19. Our findings suggest why the epidemic has continued to decline following re-opening of work and school in European countries. The superspreader phenomenon may also explain the variability in COVID-19 incidence in rural and urban areas within a country.