Background
The COVID-19 pandemic posed an unprecedented public health challenge, causing over one hundred thousand deaths in Germany alone. As elsewhere, policy-makers in Germany sought expert advice to navigate uncertainty and urgency, including through ad hoc advisory committees. We aimed to identify committees operating between 2021-2023, assess their composition, and analyse their work processes with a particular focus on structures, expert deliberations and evidence use.

Methods
We conducted a systematic document analysis of government documents and semi-structured interviews with committee members in April/May 2024. We identified documents (parliamentary inquiries and freedom of information requests) through systematic searches in digital government archives; and purposively sampled experts from identified committee member lists. Documents were analysed using abridged content analysis, and interview transcripts were analysed using codebook thematic analysis.

Results
We screened 984 documents, analysed 43 documents, and conducted 12 interviews. Ultimately, we identified six ad hoc advisory committees which met our inclusion criteria. These committees advised the German national government and the state governments of Bavaria, North Rhine-Westphalia, Rhineland-Palatinate, Schleswig-Holstein, and Thuringia. These were dominated by academic experts, especially from bio-medical disciplines. Structure of the advisory process: Consultations were direct (in person/online meeting) or indirect (written reports). Direct consultations typically included short presentations/input, followed by discussions to reach a consensus opinion. Expert deliberations drew on expert opinion, reports, pre-prints, and peer-reviewed studies. Multi-disciplinary exchange was valued but faced time constraints; opinions differed on whether a successful multi-disciplinary exchange was achieved. Reflections: Committee members were aware of the limits of their advisory role but occasionally struggled with the political nature of the work.

Conclusion
German policy-makers continued to involve ad hoc advisory committees after the first year of the pandemic. Where it was achieved and meaningful, multidisciplinary work was perceived as valuable. Political decisions deviating from expert advice required justification under certain circumstances.