CoVICIS in context: surveillance and Switzerland with Prof. Milo Puhan, MD, Ph.D., University of Zurich

Professor Milo Puhan, MD, Ph.D., serves as chair of Epidemiology and Public Health at the University of Zurich and as director of the Epidemiology, Biostatistics & Prevention Institute (EBPI). In the latest CoVICIS blogpost, Professor Puhan joins us to discuss the three prospective cohort studies, including children, adolescents, and adults, based at EBPI that are contributing to the CoVICIS project.

Why is the research being conducted at EBPI so important?

This is a genuinely rich research ecosystem serving as a responsive portfolio of surveillance and immunological research to deepen our understanding of how COVID-19 immunity varies depending on age and vaccination and infection history. This has real world implications for public health measures in response to COVID-19 outbreaks as well as providing insights into future vaccine development and evaluation.

What is the focus of the work being conducted at EBPI under CoVICIS?

The three cohort studies at EBPI include a range of age groups and patient histories to contribute to our understanding of COVID-19 immunology. In Ciao Corona, we are working with 2500 children and adolescents; the Zurich SARS-CoV-2 Cohort study (ZSAC) has enrolled 1500 people at time of infection; and the Zurich SARS-CoV-2 Vaccine Cohort Study (ZVAC) has enrolled almost 600 people enrolled at time of vaccination.

Thanks to the dynamic design of these cohort studies, which are all part of the Corona Immunitas research program at the Swiss School of Public Health (SSPH+), we’re able to investigate multiple research questions. In Ciao Corona we have studied the spread and clustering of infections at schools but also the prevalence of Long Covid among children and adolescents and the impact of the pandemic on health behaviour and health-related quality of life. In ZSAC and ZVAC, we have not only assessed immunological trajectories post-infection, vaccination, or both, but also experiences of participants of isolation and quarantine, the efficacy of the SwissCovid App, and of Long Covid.

What sort of techniques are you using in this work?

We are using a combination of laboratory tests for the immunological parameters and surveys about health behaviour, physical and mental health, and additional infections and vaccinations. This gives quite a comprehensive view of how the health is affected by infections and vaccinations.

What are some of your findings so far?

In Ciao Corona, we learned that before Omicron emerged, clustering of infections in schools happened quite rarely, which was an important finding to inform polices around schools. We were also among the first to report a prevalence of Long Covid in children and adolescents from our population based data and found that it is rarer and mostly very mild. We will soon publish a study that shows how seroprevalence and neutralisation against wildtype, delta, and omicron changed between June 2020 and June 2022.

ZSAC has turned into one of the most impactful Long Covid studies worldwide. Thanks to the population-based study design, we were able to provide valid estimates of the prevalence of Long Covid and how the symptoms develop over time up to two years post-infection. We also contributed a lot of outpatient data to the Global Burden of Disease study on Long Covid.

What is next for this work?

Follow-up activities in the cohort studies continue, this will include clinical assessments. Due to restrictions during the pandemic it was not possible to do extensive clinical assessments, but we are now planning this through a two-to-three year extension. For example, findings from the ZSAC and ZVAC study will contribute to the evaluation of three key parameters:

  1. whether the bivalent fourth dose vaccination induces protective responses against the new variants BQ.1, BQ1.1, XBB;
  2. comparison of the immune responses induced by the bivalent fourth dose to those induced by the original third or fourth dose vaccine;
  3. immune responses among individuals receiving mRNA based vaccines versus those receiving vector-based vaccines.

The planning of this analysis is currently underway, and we look forward to working with other CoVICIS partners, such as the Centre Hospitalier Universitaire Vaudois (CHUV) in Switzerland, in these next steps.