Anecdotally, we were all scared shitless in March and that’s when there was a drastic change in behavior. People stayed at home and stopped traveling. The perio

Anecdotally, we were all scared shitless in March and that’s when there was a drastic change in behavior. People stayed at home and stopped traveling. The period after which you describe is actually the period in which travel restrictions was relaxed, and people became _less_ careful. More formally, the decline after mid April was probably due to widespread immunity and weather effects. That’s only my conclusion, but based on the following: * https://www.folkhalsomyndigheten.se/publicerat-material/publikationsarkiv/e/estimates-of-the-peak-day-and-the-number-of-infected-individuals-during-the-covid-19-outbreak-in-the-stockholm-region-sweden-february--april-2020/ https://www.folkhalsomyndigheten.se/publicerat-material/publ... - A model releases mid april bases on march data which accurately placed the peak around mid april. It’s a standard SEIR model, so it predicts that it tapers off only based on population immunity. * https://news.ki.se/immunity-to-covid-19-is-probably-higher-than-tests-have-shown https://news.ki.se/immunity-to-covid-19-is-probably-higher-t... - Study showing much higher incidence of T-cell immunity in Stockholm than the incidence of individuals with anti bodies, indicating that the true population immunity is much higher than what anti body studies will show * https://science.sciencemag.org/content/369/6505/846 https://science.sciencemag.org/content/369/6505/846 - Another mathematical modeling study, based loosely on Stockholm dynamics, which demonstrates that hers immunity thresholds may be much lower when accounting for social stratification. In particular, Sweden asked ages 70+ to isolate themselves, so it’s likely the case that immunity rates are much lower in that group. * Finally, warm weather surely helped drive down the spread.