Why did we make this decision? Making decisions in times of subjective expectation building is not simple. There is either a lack of data or of a careful analysis of available data. With an incidence below 200 in Mainz and double vaccination of (most) students, we could argue to be on the safe side. It seems obvious that the pandemic is a problem because of those who are not vaccinated. Compulsory vaccination or 2g everywhere (private and on the job) would be the way out. But we are not there. And there are infections (and hospitalizations) also of those who are vaccinated twice. This is illustrated in the following figure based on data by LUA Rheinland-Pfalz.
This means that any meeting contributes to the spread of the virus. Yes, one could argue “it’s the fault of the non-vaccinated”, but this is not the full story. In any case, we do not want to encourage hundreds of students to squeeze into public transports and meet in lecture halls in times where the health system is, generally, functioning well but, in parts of Germany, at its limit. We should not wait for the situation in Mainz to be as bad as elsewhere.
It is true that the pandemic does not only lead to health costs, there are also social, mental and other costs at the same time, often resulting from contact restrictions. Hence, any decision at least implicitly attaches weights to these different aspects. Covering the need for social contacts at the private level and feeling forced to accept the increased difficulty in studying (due to fewer contacts among students), it seems wise to teach online.
Would these statements survive careful scientific analysis? Maybe, maybe not. Maybe the vaccinated are sufficiently safe and contribute very little to the overall pandemic. Yet, I am not aware of such an analysis and I do not have the time to do one on my own (or with many coauthors). Hence, yes, we make a decision with subjective probabilities without the chance to learn (sufficiently quickly). This should lead to a revival of SEU (subjective expected utility) research – but without Bayesian or other learning.
At the risk of being too prudent, no more lectures in person. And go and get vaccinated.