Texas: Over the Hump

The Summer Surge Recedes

In Texas, 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 and a fall infection surge is unlikely.  Death rates will continue to decline so long as we continue to protect the 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 reflect the likely range of outcomes for Texas.  All cases reflect dynamic age balanced mobility and social distancing (connectivity) proportionate to risk.

  • Case 1: Active June, slower July, risk balanced active Fall, schools open.
  • Case 2: Active June, slower July, more active Fall, schools open.
  • Case 3: Active June, slower July, aggressive Fall, schools open.
  • Case 4: Active June, no July slowdown, extended into Fall.

Analysis Observations

  • Texas residents are generally modulating their behavior in proportion to risk.
  • Over 24% of Texas residents have likely been infected by late July.
  • Infection rates are higher among individuals in the 20-40 age range, now approaching 35% .
  • Total deaths are likely to be in the range of 500/million (compare to NYC ~2,800/million, Sweden ~750/million)
  • Death rates continue to be heavily tilted to elderly populations.
  • 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 eventually die out, 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.

Death Trends

Case 1 reflects current mobility trends and reflects the fewest number of deaths.  Case 2, 3 have enhanced mobility in younger cohorts but since herd immunity is established the total deaths do not increase much over case 1.  Case 4 is a worst case upper bound and assumes no shift from June behavior.  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.  The CDM includes heterogeneous variations across the population for connectivity (mobility and health habits) and susceptibility resulting in a lower herd immunity threshold.  See our article: Are We Closer to Herd Immunity than Most Experts Say?



Infection Trends

In general, we see the peak of new infections in late June. 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.  As the average age of infection shifts to the lower mortality rate cohorts, we see the infection fatality rate drop to ~0.15%.  Overall, we estimate between 1% and 1.5% of the population are actively infectious in early August, and this will continue to decline rapidly.  The cumulative percent of population infected ultimately will be in the range of 30% to 40%.

 

 

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 week represents an incomplete count.

Mobility Data

Mobility trend data for Texas 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.

Summary Results

A simulation population of 2 million discrete agents is scaled by a factor of 14.3 to represent the 28.7 million population of TX.  We assume 50% of those infected are asymptomatic.




 

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