Daily Profile of COVID-19 Infections in Germany, throughout the Pandemic

Abstract

Progress of the COVID-19 pandemic was quantified, in the first instance, using the daily number of positive cases recorded by the national public health authorities. Averaged over a seven-day window, the daily incidence of COVID-19 in Germany reveals clear sections of exponential growth or decay in propagation of infection. Comparing with incidence profiles according to onset-of-symptoms shows that reporting of cases involves variable delays. Observed changes in exponential rates come from growing public awareness, governmental restrictions and their later relaxation, annual holidays, seasonal variation, emergence of new viral variants, and from mass vaccination. Combining the measured rates with epidemiological parameters established for SARS-CoV-2 yields the dynamics of change in disease transmission. Combined with the distribution of serial intervals (or generation times), the rate gives basic and instantaneous values of the reproduction number that govern development and ultimate outcome of the epidemic. Herd immunity requires vaccination of approximately seventy percent of the population, but this increases to circa eighty percent for the more transmissible Alpha-variant. Beyond this point, progressive vaccination reduces the susceptible population, and competes with the emergence of new variants. By the first Omicron wave, circa seventy percent were doubly vaccinated, with the target then standing at circa eighty percent. Combined with the distribution of times-to-death, incidence rates from onset of symptoms predict the daily profile of COVID-associated deaths and estimated case-fatality ratio. Cases are under-reported in the first wave and reflect age heterogeneity in fatalities at the second wave. In periods of low incidence, COVID mortality was one percent or less of detected infection.