Vaccine-masked spread of SARS-CoV2 in an elderly care home, and how to prevent a spill-over into the general population.

Aim: The vaccination campaign against SARS-CoV2 in Germany started at the peak of the second wave. An outbreak in an elderly care home occurred in our county at the time of the second vaccination. We describe a package of measures to control the outbreak and to prevent a spill over into the general population. Subjects and methods: After outbreak confirmation, a package of measures such as quarantine of the elderly care home, staff and visitors, and their households was implemented. By sequential testing, quarantine measures were lifted. Surveillance of staff and residents by rapid antigen test and symptom monitoring was used in parallel. Results: The outbreak was on-going for around 17 days until it was noticed by a symptomatic external staff member as index case. A total of 23 out of 96 residents (24.0%) and nine out of 114 staff (7.9%) were infected. Three residents died. Effective first-dose vaccine coverage was 85.4% in residents, 27.4% in internal, and 10.5% in external staff. Given the long latency period, the use of household quarantine prevented a spill over into the public. Already 16 days after notification of the index case the outbreak could be declared over. Conclusions: Interferences between vaccination coverage and outbreak characteristics in regard to an extended latency period were observed. Household quarantine of case as well as contact households is of increased importance in the era of vaccination to prevent further spread into the general population until population-based control measures and lockdowns can be lifted.