Ever since the first case of COVID-19 was identified in Miami on March 11th and the first death recorded on March 27th, the number of cases and deaths have increased steadily in Miami-Dade County. On March 24th, when total case count neared 500, parts of Miami-Dade began to lockdown with most of South Florida locked down by March 30th. The lockdowns effectively flattened the curve within weeks. After peaking with an average of 400 new cases per day in mid-April, the number of cases dropped slowly to near 150 per day, Miami-Dade reopened on May 18th. As it turned out this level of infection was not sufficiently low enough to safely reopen and soon after Memorial Day new cases began to surge again along with the rest of Florida.
The daily new cases for Miami-Dade (brown squares) track that of the rest of Florida (blue diamonds) very well at about 25%. Over the last 12 days the 7-day rolling average case number for the rest of Florida has peaked while that for Miami-Dade has continued to rise, albeit at a slower pace. What is surprising is that the Miami-Dade death count has deviated even more dramatically over the last 10 days – downward rather than up.
This suggests that the case fatality rate (CFR = deaths/cases) for Miami-Dade has all of a sudden improved dramatically for Miami-Dade versus the rest of Florida. It is not clear to us why this should be the case. The strongest driver of CFR is age, and the median age of cases in Miami and the rest of Florida had dropped in June as more young adults ventured out and partied with poor masking or social distancing. However, the median age has crept back up for both Miami and the rest of Florida over the last 5 weeks. Other comorbidities and demographic factors do not appear to have changed significantly from spring to summer to justify this improvement in CFR for Miami.
So either Miami is vastly undercounting their COVID-19 hospitalizations and deaths recently due to abnormally high volume constraints, or they have found a miracle therapeutic that vastly improves survival rates from a May peak of 8% (=16/200) to 0.6% (=15/2600) now. We are estimating that the true CFR for Miami-Dade is 1.4%, lower than May’s 8% due to wider testing of asymptomatic and mildly symptomatic cases, younger patients, and better therapeutics, but higher than 0.6%. Death counts will catch up to this estimate over the next few weeks. Moreover, unless Miami-Dade reverses much of its reopening steps to mitigate the spread, both cases and deaths could continue to rise. Note that the total case count is now 200 times higher than when it last decided to lock down Miami-Dade.