"When is the 2nd wave?"
No idea, with the government's current approach much will depend on how many people have already been exposed to the virus, how many have developed immunity (likely all those who have had the virus, at least for some period of time), and crucially how many people are still susceptible.
Susceptibiliy is key. I keep hearing reports of "T-cells this" and "T-cells that" and while the research is all very interesting (and may have huge significance) some of the authors of such papers (Shane Crotty for one) are right to note that we do not yet know how relevant this is clinically.
If it is found that a much lower proportion of the population are still susceptible than is thought then there may not be a "2nd wave".
If there is a large proportion of the population still susceptible then a "2nd wave" is inevitable if things open up and people mix. What a "2nd wave " looks like in terms of cases, hospitalisations, deaths no one knows. There is a larger number of tests taking place now and a different section of the population can now access a test.
Just because we see a rise in cases it might not necessarily lead to subsequent increase in hospitalisations and deaths. Everything has to be looked at in context. Far too many people seem unable (or unwilling) to do this.
Does anyone know how many people have had the virus or are still susceptible? No. No one does and that's the problem. The way forward would ideally be very different depending on the answer.