A Disease Suppression Strategy in Action: The Impact of Non-Pharmaceutical interventions in the COVID-19 pandemic in Denmark.

When a new pandemic virus emerges in a naive population the only control options are Non-Pharmaceutical Interventions, NPI's, until vaccines or effective treatments become available. Here we report on the Danish suppression strategy and use of a combination of NPI's with a notable absence of extremely strict measures (such as stay-at-home orders). Only 7% were infected (serological evidence) in the first year of the pandemic, compared to ∼50% in Lombardy in the first wave alone. This low attack rate was accomplished by initial rapid intervention with a free-of-charge mass testing program beginning in October 2020, a strong digital data infrastructure, timely contact tracing and voluntary home isolation, real time reporting of surveillance data and a high degree of public trust. The individual contribution of each NPI to the pandemic control is difficult to assess; yet evidence points to the mass testing program as being particularly effective in removing infected individuals from the pool. In January 2021 vaccines became available and 96% of Danes over 50 years of age were vaccinated twice with a mRNA vaccine by summer. On February 1, 2022, while facing the Omicron variant and with the elderly newly boosted, Denmark became the first country to drop all NPI's. A few months later, 70% of the population had been infected with Omicron, showing the SARS-CoV-2 transmission potential when unmitigated. Denmark was only close to Intensive Care Unit capacity during the 2nd wave in winter 2020-2021 when 5% of the population were infected. In conclusion, the effectiveness of the combined NPI's is evident due to the low (<10%) attack rate in the first two waves before vaccines became available, far from the experience of unmitigated COVID-19 in Lombardy in spring 2020 with ∼50% attack rate with a high morbidity and mortality.