Covid-19 hardly mutates and people who were exposed to SARS 17 years ago have immunity to covid today. So yes, it’s pretty safe to say there won’t be a second wave of any significance. This was known since Februari and I don’t understand why you would think this disease will be seasonal when it isn’t anything like the seasonal viruses we know that mutate and don’t trigger good immune responses.

(It is seasonal in the sense that the R0 is higher in the winter when people are cooped together, but once you've got sufficient exposure in the community a second wave won't happen regardless)