Dear Dominik, thank you very much for taking the time for this interview.

Would you like to tell us briefly what your background is and where your current research focus lies?

Gladly. I am an epidemiologist and a specialist in prevention and public health. I specialize in public health issues, which of course became particularly important during the pandemic. In my research here at the institute, I deal with various topics. On the one hand, these include the treatment and early detection of cancer. On the other hand, the consequences of the coronavirus pandemic - for example, Long Covid - and the coronavirus vaccinations are also important topics for me.

Currently you are involved in the Zurich SARS-CoV-2 Vaccine Cohort Study (ZVAC), which is investigating the immune response of vaccinated individuals. Could you give us a brief overview and explain what the goals of this study are?

The Zurich SARS-CoV-2 Vaccine Cohort Study is an observational study of individuals who have received a coronavirus vaccination at the reference vaccination center. A total of 575 individuals, who have received either the Moderna, Pfizer/BioNTech or Janssen/Johnson & Johnson vaccine, are participating. We had three main objectives with the study: First, we wanted to investigate how common and severe the side effects of the vaccines were. Second, we wanted to find out how the immune response develops after vaccination and in the longer term. And finally, we wanted to investigate how good the protection of the vaccinations against coronavirus infections is.

What were the most important insights you found? What surprised you personally the most?

I think it was very important to study how common side effects actually are after coronavirus vaccination and how severe they are. To do this, we used symptom diaries. We were able to show that mild symptoms such as pain at the injection site or flu-like symptoms are common. In contrast, severe side effects such as allergic reactions or those that resulted in hospitalization were rare. These are important data because they are otherwise rarely available in this form - only very few side effects are publicly reported, so their frequency may be underestimated. In addition, our studies on the immune response were also very important. What amazed me, however, was the great commitment of the study participants, who were willing to support us in our research.

Since January 2021, the Institute of Epidemiology, Biostatistics and Prevention (EBPI) of the University of Zurich (UZH) has acted as the reference vaccination center for the canton of Zurich and is "the home" of the ZVAC study. Since then, various vaccines have been licensed, with ongoing changes in vaccination recommendations. How did you experience working on the study during such a dynamic time?

It was an intensive but also very exciting time. There were many uncertainties and the recommendations were constantly adapted to the latest state of knowledge. The Zurich Coronavirus Vaccination Study provided an ideal basis to address the scientific and health policy issues. This allowed us to provide the health authorities - i.e. the Department of Health of the Canton of Zurich and the Federal Office of Public Health - with exactly the information they needed. In this way, the findings of the study were incorporated directly and quickly into the recommendations. For us, it was of course very interesting to be directly involved in this and to make a contribution - and at the same time to be in contact with our study participants and to answer their questions.

Previous results of the study have already been published. It shows that almost all study participants (99.1%) developed an immune response against the virus within three months. Was such a high number to be expected?

We saw early on in the study that the immune response to the vaccines was very strong. In our other study with people who had been infected with coronavirus, after 3 months, antibodies were only detectable in about 85% of the participants. So it showed us that the immune response was much stronger after vaccination than after infection. That was the hope, of course, and it was good to see that confirmed. Thus, vaccination was able to achieve good protection against severe disease in the vast majority of people.

It was found that the two mRNA vaccines from Pfizer/BioNTech and Moderna elicited a slightly stronger immune response on average than the vector vaccine from Janssen/Johnson&Johnson. Were there differences in the immune response in the different age groups?

It was known early on that the mRNA vaccines had a stronger effect than the vector vaccines. We were able to observe that in our study as well. We also found some difference between age groups. Younger individuals often had a more pronounced antibody response. However, this was to be expected, and protection against severe disease was good across all age groups.

Can comparisons already be made between the immune response of individuals with COVID-19 infection and individuals who have received COVID-19 vaccination?

We are currently in the process of conducting these studies. We know that the more severe someone got COVID-19, the stronger the immune response was. The mRNA vaccines triggered even stronger immune responses. In part, this is related to the fact that people received two doses of the mRNA vaccines. Meanwhile, the immune response after the Janssen/Johnson&Johnson single vector vaccination was about the same as we observed for coronavirus infections.

How do you think this study contributes to our understanding of vaccine-induced immunity?

With the pandemic, there was a very high level of public interest in immunity and the effect - but also the side effects - of vaccines. Overall, this has brought many insights that are very valuable for our understanding of vaccines and the immune system. We have already gained many important insights and have been able to publish them or pass them on to the health authorities. Of course, we hope that our study will continue to make a contribution in the years to come.

What do you think are possible implications of the study findings for policies or approaches in public & global health?

I think we were certainly able to show how important population-based studies and research projects can be in supporting health policy decisions and informing the population. In a pandemic, there are always many uncertainties and fears. It is important to communicate these uncertainties transparently and to establish a good basis as quickly as possible to scientifically clarify the important questions. Although we naturally hope that something like this will not happen again so soon, the expertise gained will be very valuable for future crises in the field of public and global health.

Thank you so much for this interview and our work here at EBPI!

Interview: Sofia Ricar