The Summer Surge Recedes
In Florida, as in many states, there was abundant activity in June, largely among a younger cohort, and this caused a significant summer surge. Once the virus penetrates deeply into this cohort, significant progress toward herd immunity is established, rendering a fall infection surge unlikely. Death rates will continue to decline so long vulnerable and at risk elderly individuals continue to take precautions proportionate to their risk factors as described in our article: Rational Policy Strategies for the COVID-19 Pandemic.
Recovery Model Case Studies
We examine 4 recovery models which bound the range of outcomes for Florida. Case 1 and 2 reflect dynamic age balanced mobility and social distancing (connectivity) proportionate to risk. Case 3 and 4 illustrate the effect of early mobility among elderly populations.
- Case 1: Active June, slower July, flat mobility extension into the Fall, schools open.
- Case 2: Active June, slower July, increasingly active Fall, schools open.
- Case 3: Active June, slower July, active Fall, schools open, more active elderly (not recommended).
- Case 4: Active June, slower July, very active Fall, schools open, very active elderly (not recommended).
- Florida residents are generally modulating their behavior in proportion to risk.
- There was little reduction in mobility in response to the summer surge in July.
- Over 25% of Florida residents have likely been infected by mid August.
- Infection rates are high among individuals in the 20-40 age range, ~35% in mid August.
- Total deaths are ultimately be ~750/million (compare to NYC ~2,800/million, Sweden ~750/million)
- Death rates continue are strongly biased toward elderly populations.
- Florida’s elderly demographic pushes the overall death rate higher than younger states.
- The Infection Fatality Rate is currently in the range of 0.25% and will rise if elderly become active too early.
- Returning children to school and extracurricular activities do not cause a significant increase in deaths or infections.
- Risk proportional mobility lowers herd immunity threshold; reached when 40-50% of 20-40 year olds are infected.
- Vulnerable and elderly populations are at risk and should continue to take precautions and avoid high risk situations.
- The summer surge will die out in the fall, we will not see a returning infection peak if elderly and vulnerable are protected.
- Improvements in therapeutic methods have significantly reduced the mortality rate, we assume a 40% reduction since March.
Case 1 reflects current mobility trends and reflects the fewest number of deaths. Case 2 has enhanced mobility in younger cohorts but since herd immunity is established the total deaths do not increase much over case 1. Case 3 and 4 are to show the effect of increased mobility among elderly populations; not likely if elderly populations continue to be cautious. Until the infection has damped down, elderly and vulnerable people should continue to avoid risky situations and practice social distancing. In all cases the infection dies out by winter. Our COVID Decision Model (CDM) results are compared to the current IHME predictions for reference (only through November); our Case 2 scenario matches the IHME mean. The CDM includes heterogeneous variations across the population for connectivity (mobility and health habits) and susceptibility resulting in a lower herd immunity threshold and an ultimate flattening of the curves. A recent MIT article describes this effect: Population immunity is slowing down the pandemic in parts of the US. See our article for a more technical assessment: Are We Closer to Herd Immunity than Most Experts Say?
In general we see the peak of new infections in early July. The percentage of the population currently infected shows a peak a couple weeks after the peak of new infections. With the delay from infection to test, and from test to results, we would expect to see the peak of positive tests to be later in July and early August. As the average age of infection shifts to the lower mortality rate cohorts, we see the infection fatality rate drop to in the range 0.2 to 0.25%. The cumulative percent of population infected ultimately will be in the range of 30% to 35%.
Date of Death Extraction
Determination of actual date of death is critical to calibration of the analysis. The graph below shows the derived date of death the reported death date data sets found at the COVID Tracking Project. Our approach is far more accurate than a rolling average of reported deaths and is detailed here: Reported versus Actual Date of Death. The most recent 2 weeks represent incomplete counts.
Mobility trend data for Florida from the IHME indicates a minor slowdown in July following a June peak. Mobility data does not include the effects of enhanced personal hygiene or indoor social distancing, but does indicate a general trend. We stratify these trends by age group in our analysis.
A simulation population of 2 million discrete agents is scaled by a factor of 10.65 to represent the 21.3 million population of Florida. We assume 50% of those infected are asymptomatic.