[Spreading Dynamics of the Alpha and Beta Virus Variants of SARS-CoV-2 at the Beginning of Their Appearance in the City of Cologne in January and February 2021].

background and aim of the studyConstantly changing virus variants of the novel coronavirus SARS-CoV-2 pose major challenges to the healthcare system. The aim of the present study was to analyse major outbreaks of the alpha and beta variants in Cologne in order to enable effective and rapid response to new virus variants in future pandemics as well as to derive targeted measures to combat the pandemic.

methodsIn the observation period from January 22 to February 23, 2021, all individuals testing positive for SARS-CoV-2 and their contact persons who were reported to the Cologne Public Health Department were interviewed by employees of the Public Health Department over the telephone. On the one hand, these data formed the basis for the epidemiological and descriptive comparison of the alpha and beta variants to the previously dominant wild type. On the other hand, they were also the basis for the graphical processing of clusters formed by the two virus variants in the form of so-called timelines. For the present work, all clusters with ≥10 individuals were taken into account for the period under consideration.

resultsOf the 3780 individuals that tested positive for SARS-CoV-2 in Cologne during the observation period, 818 cases were due to the virus variants alpha and beta. The alpha versus the beta variant spread quickly in Cologne despite strict non-pharmaceutical interventions. As part of the cluster analysis, five major outbreak were identified in Cologne during the observation period. The alpha variant clusters included two daycare centers and one monastery, while the beta variant clusters included a communal accommodation for refugees and an old people's and nursing home. With the help of cluster analysis, the core role of the spread of the virus variants examined was shown, especially in the context of the home setting. In addition, a high proportion of cases of unknown infection site/contact was found for the wild type and alpha variant.

conclusionCluster analyses are an extremely useful tool in the determination of infection sites/contacts and transmission paths as well as in determining existing protective measures and hygiene concepts. Since clusters are to be regarded as the most unfavorable spread scenario, cluster analyses provide important suggestions for modifying further action for both this, as well as for future pandemics.