Improved tracking of exposure abroad is clearly relevant for the containment of COVID-19, as the arrival of newly infected individuals endangers the pandemic control (1, 2), especially if the number of undetected cases is high.
In a parallel publication, we examined the effects of such influx events according to the different levels of workload of the health authorities (test, trace, and isolate [TTI]) and were able to clearly quantify that a tipping point occurs when there are too many undetected carriers with viral loads (1).
In this current study, however, the reason behind the change in case numbers does not matter.
In addition, we find no evidence that the number of undetected cases increased significantly from July to September, despite a doubling of case numbers among people younger than 60 years (3). We also do not know of any evidence showing that the majority of asymptomatic returning travelers were able to remain undetected. The effects that you describe on the number of undetected cases should have shown up as unexpected deaths by September at the latest (3).
Returning travelers contributed to an increase in the number of cases, but not to a measurable increase in the number of undetected cases.
References
Footnotes
Conflict of interest statement:
The authors of both contributions declare that no conflict of interest exists.
References
- 1.Priesemann V, Balling R, Brinkmann MM, et al. An action plan for pan-European defence against new SARS-CoV-2 variants. Lancet. 2021;397:469–470. doi: 10.1016/S0140-6736(21)00150-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Contreras S, Dehning J, Loidolt M, et al. The challenges of containing SARS-CoV-2 via test-trace-and-isolate. Nat Commun. 2021;12 doi: 10.1038/s41467-020-20699-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Linden M, Dehning J, Mohr SB, et al. Case numbers beyond contact tracing capacity are endangering the containment of COVID-19. Dtsch Arztebl Int. 2020;117:790–791. doi: 10.3238/arztebl.2020.0790. [DOI] [PMC free article] [PubMed] [Google Scholar]