My hypothesis is that herd immunity (mainly via vaccinations) is a huge factor but we have to consider how many of our infections are breakthrough infections or caught by people who had covid before.

I do wonder if opening up in the summer show the benefits of ventilation and possibly UV light from the Sun?

Though my concern is what if we have to lockdown because of people who are unvaccinated getting it and ending up taking up hospital beds? Would be annoying for them to drag us down with them. I would imagine the vaccinated people in Austria hating the unvaccinated.

Also on a sympathetic level, it would be sad to see some people get the virus (and possibly go to hospital) via the breakthrough infections