Background: In 2018, a hospital-based surveillance system for influenza (CH-SUR) was established in six tertiary care hospitals in Switzerland. From March 2020 onwards, this surveillance system was expanded to include more institutions, as well as COVID-19. Aim: To evaluate quantitatively and qualitatively the surveillance system CH-SUR. Methods: All patients admitted to one of the participating centres for more than 24 hours and who had a laboratory-confirmed influenza virus or SARS-CoV-2 infection were included in CH-SUR. For all cases, we evaluated the quality of the CH-SUR data, including timeliness and completeness of reporting. A qualitative survey among CH-SUR stakeholders assessed perceived importance, understanding, reliability and adaptability of CH-SUR. Results: Up to 20 centres participated in CH-SUR. Between December 2018 and October 2023, 7,375 cases of influenza were reported and between March 2020 and October 2023, 49,235 cases of COVID-19 were reported to CH-SUR. During the COVID-19 pandemic, time to data entry and completeness improved over time; the median delay of data entry in CH-SUR was 5 days (IQR=2-23) for COVID-19 and 4 days (IQR=2-15) for influenza during the period 2018-2023. The completeness of variables was high (99.4%), with the exception of COVID-19 or annual influenza vaccination status (respectively 15% and 72% of 'Unknown' responses). Stakeholders perceived the system as important, relevant, understandable and adaptable. Conclusion: CH-SUR has provided critical epidemiological and clinical information on hospitalised influenza and COVID-19 cases across Switzerland during the pandemic. Our evaluation highlighted the importance and relevance of this system among CH-SUR stakeholders, as well as its importance for preparedness and response to future infectious disease outbreaks.

The authors have declared no competing interest.

We acknowledge that this study was made possible through the funding and supervision provided by FOPH and the Swiss National Science Foundation (grant no 31CA30_196270).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The CH-SUR system was approved by the Ethics Committee of the Canton of Geneva, Switzerland (CCER 2018-00577, and CCER 2020-00827). Data collection was also approved by all local ethics committees. For the qualitative survey, all participants were informed about the purpose of the survey, the voluntary nature of their participation, and the confidentiality of their responses.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

CH-SUR data can be accessed upon request through the CH-SUR scientific committee's approval process.