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. 2021 Nov 2;9(11):1267.
doi: 10.3390/vaccines9111267.

COVID-19 Breakthrough Infections and Transmission Risk: Real-World Data Analyses from Germany's Largest Public Health Department (Cologne)

Lea Hsu  1   2 , Barbara Grüne  1 , Michael Buess  1 , Christine Joisten  1   3 , Jan Klobucnik  1 , Johannes Nießen  1 , David Patten  1 , Anna Wolff  1 , Gerhard A Wiesmüller  1   2 , Annelene Kossow  1   4 , Julia Hurraß  1
Affiliations

COVID-19 Breakthrough Infections and Transmission Risk: Real-World Data Analyses from Germany's Largest Public Health Department (Cologne)

Lea Hsu et al. Vaccines (Basel). .

Abstract

Background and methods: Vaccination is currently considered the most successful strategy for combating the SARS-CoV-2 virus. According to short-term clinical trials, protection against infection is estimated to reach up to 95% after complete vaccination (≥14 days after receipt of all recommended COVID-19 vaccine doses). Nevertheless, infections despite vaccination, so-called breakthrough infections, are documented. Even though they are more likely to have a milder or even asymptomatic course, the assessment of further transmission is highly relevant for successful containment. Therefore, we calculated the real-world transmission risk from fully vaccinated patients (vaccination group, VG) to their close contacts (CP) compared with the risk from unvaccinated reference persons matched according to age, sex, and virus type (control group = CG) utilizing data from Cologne's health department.

Results: A total of 357 breakthrough infections occurred among Cologne residents between 27 December 2020 (the date of the first vaccination in Cologne) and 6 August 2021. Of the 979 CPs in VG, 99 (10.1%) became infected. In CG, 303 of 802 CPs (37.8%) became infected. Factors promoting transmission included non-vaccinated status (β = 0.237; p < 0.001), male sex (β = 0.079; p = 0.049), the presence of symptoms (β = -0.125; p = 0.005), and lower cycle threshold value (β = -0.125; p = 0.032). This model explained 14.0% of the variance (corr. R2).

Conclusion: The number of transmissions from unvaccinated controls was three times higher than from fully vaccinated patients. These real-world data underscore the importance of vaccination in enabling the relaxation of stringent and restrictive general pandemic control measures.

Keywords: COVID-19; SARS-CoV-2 pandemic; SARS-CoV-2 transmission; breakthrough infections; vaccination.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Operational procedures in the Cologne Health Department and Cologne laboratories.
Figure 2
Figure 2
Occurrence of the different virus variants during the observation period in Cologne.
Figure 3
Figure 3
Flow chart of the study population; VG = vaccination group, CG = comparison group, CP = contact person; grey = data not shown.
Figure 4
Figure 4
Factors influencing transmission of CPs; binary logistic regression.
See this image and copyright information in PMC

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