COVID-19 Odds

Quantitative analyses on the global coronavirus pandemic

COVID-19 Pandemic in Florida – Wave #5

Florida just reported 110k new COVID-19 cases for the past week – nearly equal to the all-time high we had predicted Florida (FL) will set by early August.  Florida continues to lead the USA higher in COVID-19 cases although Texas Governor Abbot is trying very hard to catch up by banning mask and vaccine mandates.  The Delta variant is so ferocious even CA and NY are seeing exponential growth as are nearly all 50 states in the USA.  But Florida continues to lead and may be a harbinger for what will happen to the USA in August.

There are several reasons why Florida is doing so well in this race to the bottom:

1.     FL has been very welcoming to all variants since Governor DeSantis removed all local COVID-19 mitigations on May 3.

2.     FL stopped daily reporting and possibly tracking of COVID-19 cases on June 3 – suggesting the pandemic is over.

3.     The Governor stopped responding to the COVID-19 crises even as cases began to rise 7 weeks ago and shifted his focus to his potential presidential run

This has left Florida wide open and blind to the COVID-19 Delta variant just as it began to take over the USA 2 months ago.  Reporters, scientists, and citizens clamored for more information but the Governor just seem to double down on his obstruction efforts.  His latest attempt to help the SARS-CoV-2 virus is to declare war on municipalities that want to restore mask mandates for schools.  In the meantime, he continues to turn a blind eye to the burgeoning crisis as exemplified by the weekly FL DOH (Department of Health) COVID-19 reports.  These weekly reports are totally inadequate and obscure the real picture of the fast-developing crisis in FL. 

As a small but indicative example of misleading the public, we look at the summary data from these weekly DOH reports.

report dateCum casecalc diffpre wk casecum deathcalc diffpre wk deaths
30-Jul       2,590,699       110,724       110,477       39,079        409        108
23-Jul       2,479,975         73,166         73,199       38,670        282          78
16-Jul       2,406,809         45,449         45,604       38,388        231          59
9-Jul       2,361,360         23,747         23,697       38,157        172          32
2-Jul       2,337,613         15,684         15,978       37,985        213          48
25-Jun       2,321,929         11,048         11,873       37,772        217          44
18-Jun       2,310,881         10,095         10,629       37,555        290          43
11-Jun       2,300,786         12,157       37,265          40

The weekly cumulative cases and per week cases data make sense (cols 2-4 in the table above).  Subtracting the current week’s cases from the previous week’s cases yield the increment for the week (roughly as the data is sometimes corrected/updated).  This number increased by a factor of 11.1 over the last 6 weeks and should scare everyone including the Governor.  Subtracting the cumulative death numbers each week from the prior also yields a rising trend over the last 3 weeks – lagging the rise in cases by 2-4 weeks as it always has.  But the last column seems to try to understate the problem.  For example DOH reports 108 deaths for the previous week when 409 was the more indicative number of deaths.  The reason for this difference (unexplained) is that the DOH 108 number reflects only deaths that occurred AND were reported for that week.  Since deaths lag by as many as 10 weeks in FL, the initial report of this number is always too small and not very meaningful until the full number emerges 10 weeks later which may be 400-500.  The DOH used to explain this more clearly in their daily reporting but not in these truncated and censored weekly reports.  Thus a misleading impression is left to the reporters and other readers of this report.  This faux pas has potentially significant consequences because many doctors and hospitals are finally seeing a resurgence of vaccinations over the last few days as people see rising deaths.  Reporting the true death count trend could have scared more fence-sitters into action sooner and end this pandemic sooner.

Our prognosis for FL is generally optimistic.  Because the Delta variant spreads so quickly and ferociously we expect the current surge to top out within two weeks.  The recent CDC recommendation to reinstate indoor masking will help.  The recent decision by POTUS, Disney, and other major companies to mandate vaccinations for their employees or be subjected to more testing is another step in the right direction.  More people scared into vaccinations buttress this optimistic view.  Countering this is our fear that the Governor by fighting schools, cruise liners, and other companies will provide more kindling for the FL COVID-19 fire and prolong this current surge – infecting hundreds of thousands of unvaccinated kids as FL schools start to reopen in 10 days.  Few of these kids will die but a large number may succumb to MIS-C and long COVID symptoms.  This is an extremely scary scenario that may play out if the Governor is successful in his efforts to stymie and confuse schools, parents, and other Floridians.  

COVID-19 Breakthrough Cases

The CDC in the USA continues to lag the best-in-class by requiring minimal genetic testing and tracking of COVID-19 cases compared to the UK or Israel.  This has led to slower identification and monitoring of COVID variants and how mutations can change their infectiousness and speed of spread.  To date, the CDC monitors only a limited sample of those who are fully vaccinated and have serious hospitalizations and deaths, dropping their initial request for states to monitor all “breakthrough” cases.  This data is only voluntary – passive reporting by the county health departments that decide to participate.  This has led to erroneous conclusions about the speed and seriousness of the current COVID-19 Delta surge.

One very bad statistic that is often quoted is this: As of July 12, of the more than 159 million fully vaccinated people in the USA only 5,189 were ever hospitalized or seriously ill, and only1,063 died from COVID-19.  The conclusion that only 0.0033% of those fully vaccinated will get seriously ill (or 0.0007% will die) from COVID-19 is totally misleading.  The reason is that only a small percentage of fully vaccinated folks have been exposed for a short amount of time to COVID-19 in general and the Delta variant in particular.  Until recently the community exposure was only a few percent.  The community spread is now approaching 10% again as testing increasingly returns positive results.  Another popular statement is that of the 170k Americans who have died from COVID this year only 1k were fully vaccinated.  Since this is less than 1% the conclusion is that the Delta surge is a pandemic of only the unvaccinated.  Again this is extremely misleading since the percent of all Americans fully vaccinated at the beginning of the year was very small and only approached 50% recently.

A more relevant and accurate way to assess breakthrough cases and deaths is to look at what has happened recently.  Using the CDC data for the week of 7/13-7/19, we note that 725 serious hospitalized cases and 78 deaths were reported as breakthroughs likely associated with COVID-19.  This should be compared with the 1,978 COVID deaths reported for the week.  Thus 4% (= 78/1978) of all deaths were breakthrough deaths.  These deaths resulted from the infected population over the previous 1-4 weeks which we estimate to be 110,000 in total (see Table below).  This makes the overall lagged case fatality rate, CFR, 1.8% (= 1978/110000).  Segmenting this data into fully vaccinated and unvaccinated folks we estimate that the CFR for fully vaccinated people is 0.3%, far better than the 2.4% experienced by the unvaccinated – a clear incentive to get vaccinated.  This segmentation data also suggests that 30k breakthrough infections occurred over the past 1-4 weeks.  Most of these were asymptomatic or mildly symptomatic so few noticed them and no health authorities tracked them. Anecdotal reports of breakthrough cases among athletes and select populations were dismissed since they were nearly all mild. 

vaccinated unvaccinated            total
Infected (lagged)30,00080,000110,000
Hospital admits7259,27510,000
Deaths (7/13-7/19)781,9001,978
CFR (lagged)0.3%2.4%1.8%

The mRNA vaccines are a remarkable scientific achievement, and much better than most vaccines, but they are not perfect and should not be oversold as such.  They reduce the chance of death by 91% but may only reduce the chance of infection by 40%.  Many fully vaccinated people can still get the virus but their immune systems will have been primed to reduce the probability of serious illnesses and deaths (but not eliminate it).  They are also less likely to carry a viral load large enough to transmit as effectively as unvaccinated people (although some say the Delta variant can increase viral loads a thousandfold), but there is little doubt that they can transmit the Delta variant.  In fact, that they lead to so many asymptomatic cases may be what is exacerbating the latest surge because of the prevalence of silent carriers.  Thus the CDC miscommunicated recommendation to discard indoor masking without verification should be corrected immediately.  Masking and/or social distancing should be recommended outdoors.  Vaccinations should be required for all Federal personnel and for entry into Federal facilities.  The best way to ensure compliance is to require vaccine passports.  Each day’s delay in implementation is costing thousands of Americans their lives and livelihood.   

COVID-19 Surge #5 in the USA – How Deadly?

Since the COVID-19 pandemic began a year and a half ago, there has always been a debate about how serious COVID-19 really is compared with common seasonal flu which kills tens of thousands each year.  Even after more than 600,000 Americans have died and as cases are soaring again the hope is that the death rate in the USA will not be as bad now that half of all Americans have been fully vaccinated. 

The coincident death rate (daily deaths divided by daily new cases) allows us to gauge how deadly a disease is but it has several shortcomings principally due to the fact that deaths lagged infections by a couple of weeks as hospitals and doctors struggle to save patients’ lives.  As reported death counts have an additional problem since some counties and states take several weeks to fully record and report the cause of death.  But since reported death rates are a convenient measure of disease severity and effectiveness of treatment we proposed to use a lagged case fatality rate (CFR = daily deaths divided by an infection curve weighted average of reported cases over the prior 4 weeks).  This adjusted CFR is still just an estimate (since both case and death counts are widely believed to be undercounted), but it allows us to forecast future death counts and to assess whether hospitals and doctors were swamped and patients were unnecessarily lost due to poor planning and shortage of supplies (as they were during the early stages of the pandemic when this ratio was higher than 10% in the USA), and whether treatment methods have improved or not. 

The CFR decreased significantly throughout 2020 even as the USA saw ever-larger surges in infections than the original one last spring.  One major reason is that testing improved so more cases including mildly symptomatic and asymptomatic cases were identified (and the CFR denominator was better measured).  Another is that more effective therapeutics and equipment became available and improved outcomes.  A third reason is that more seniors more vulnerable to COVID-19 took precautions not to get infected and the average age of hospitalized patients declined. 

Unfortunately, the progress seen in 2020 appears to have stalled in 2021 with CFR consistently near 1.8% even though the expectation is that the CFR should have improved further as vaccines became widely available.

  1. As vaccines were rolled out and made available primarily to frontline workers and seniors and those with comorbidities a large part of the vulnerable population should have been removed from the infection pool
  2. The average age of hospitalized patients continued to decline and the very strong CFR age effect should have driven the overall CFR down. 
  3. Improved therapeutics became more widely available.  While monoclonal antibodies were introduced last year, they were only available in limited quantities and that supply constraint should have eased in 2021.

Countering these positive trends were some negative ones:

  1. Many falsely believed that vaccinations protected them fully when the truth is that 95% protection is extremely good but not perfect.  The vaccine made an 80yrs old male 10-20 times less likely to die – about the same vulnerability as an unvaccinated 60yrs old female with 1.5% mortality.  More people letting down their guards may have contributed to keeping death rates high
  2. The new delta variant may be more lethal than the original.  It is known to be 2.3 times as contagious but most scientists believe that it is not any more lethal though no one really knows yet.  
  3. Easing or removal of many mitigation measures such as masking indoors in mid-May by the CDC which mostly impacted infection rates but may have increased viral loads transmitted as well 

The lack of an improvement in CFR is extremely disappointing and troublesome. In the UK where there were more mitigation measures in place to protect the unvaccinated and slow the spread, a significant portion of the infections were breakthrough cases with lower fatality rates helping to bring their overall CFR down.  With the removal of nearly all mitigation measures on 7/19/21 more of the UK infection pool will be the unvaccinated (plus vaccinated but immunocompromised) who will suffer higher fatality rates worsening overall CFR for the UK. 

In the USA, most states removed their mitigation measures this spring so the infection pool remained dominated by the unvaccinated and the CFR has remained high.  We are forecasting that 8,000 Americans will die over the next 4 weeks due to cases and hospitalizations already in the queue.  About 400 of these will be “breakthrough” deaths of fully vaccinated people.  We are forecasting a modest improvement in the USA CFR to 1.5% as masking is reintroduced.  Nevertheless, this fifth wave could be nearly as deadly as the previous two and kill tens of thousands of Americans unnecessarily.   

COVID-19 Vaccines Work Great but Not for 10M Americans

There is no doubt that COVID-19 vaccines are working beautifully to drive down COVID-19 cases in the USA.  With 170M Americans or 51% having had at least one dose of the vaccine, cases in the USA have dropped to a 14-mo low of 5 per 100,000.  

However, there is a significant subpopulation of the USA, 10M or 3%, who may not be fully protected by the vaccines.  These include those (>6M) that are taking immunosuppressive drugs such as steroids used to treat organ transplants, cancers, or other medical conditions, and those who have compromised immune systems due to blood cancers and other diseases.  The original clinical trials for vaccines specifically excluded people who were taking immunosuppressive drugs to get their impressive 95% efficacy results.  Real-life studies were equally impressive since less than 3% of those sampled were immunocompromised.  More targeted real-life studies with immunocompromised patients show more disappointing results.  One JHU study of implant patients showed 46% had no antibodies after being fully vaccinated.  Another study from Israel showed that only 40% of all CLL cancer patients produced any antibodies after being fully vaccinated. 

There are no public databases that track the large scale response of the immunocompromised to vaccines but it is well known that a higher percentage of seniorsincreasing with age, are immunocompromised compared to younger adults.   We suspect that this is one of the reasons why even though senior compliance with vaccinations is very high (86% of everyone over 65yrs in the USA have had at least one dose) seniors continue to get infected and die from COVID-19.  In Florida (FL), the relative infection rate for seniors after falling to a low in April with the success of the Seniors First program is now close to what they were before mass vaccinations began in January, even though a much higher percentage of seniors (88%) have now been vaccinated than the general population (49%).  As more of the rest of the population gets vaccinated this relative contagiousness for seniors may rise further.  The optimistic view is that even for those who have no detectable levels of antibodies from B-cells, other parts of the body’s immune system such as T-cells have been trained after vaccination to fight SARS-CoV-2.  This would be unlikely if the trend we see for seniors in FL continues to worsen. 

What is the solution for this vulnerable part of the population who already have a much higher risk for hospitalization and death due to SARS-CoV-2 and who now seem to gain less from excellent vaccines?  Some people have proposed a third vaccine dose and have seen some success with it.  Others have proposed stopping immunosuppressants temporarily to allow the vaccine to do its work at generating antibodies.  Others have proposed using monoclonal antibodies such as REG-COV as prophylactic.  In the meantime the CDC’s new mask guidance does not apply to this vulnerable group who must continue to mask, social distance, and practice good hygiene until herd immunity is reached.  This means that we must redouble efforts to convince the fence sitters that getting the vaccine can save not just their own lives but the lives of friends and families who may be immunocompromised.

End of the COVID-19 Nightmare in the USA?

Covid-19 daily cases started rising again about 4 weeks ago signaling the beginning of a fourth wave in the USA.  However, over the last week cases have resumed declining cutting short the fourth wave.  Is this a real indication of light at the end of the tunnel or are we just seeing the headlight of the oncoming train?

42.2% of the USA has been vaccinated with at least one shot to date (green part of the graph below).  This seems to be too low to meet the 70%+ threshold that is generally believed to be the vaccination level needed for herd immunity.  However, we have always asserted that while rigorous herd immunity with vaccines is the most desirable goal, effective human immunity may be reached earlier and allow the USA to flatten the COVID-19 infection curve.  Effective human immunity is a combination of natural immunity gained through infection by the SARS-COV-2 virus, vaccine immunity, and behavior immunity due to citizens rigorously practicing masking, social distancing, and isolation as necessary.

Natural immunity has been acquired by 32.8M Americans that have been confirmed as infected to date (red part of graph above).  A much larger portion of Americans had been exposed to the virus but had asymptomatic or milder cases of COVID-19 who did not get tested because of lack of available and/or timely PCR tests (dark blue part of graph above).  This could have been as large as 8X the confirmed population a year ago during the first wave when the USA was ill-prepared.  Over time, this factor has declined with wider and more timely testing and we suspect it is just 2X confirmed cases now nationwide.  Large studies have confirmed that natural immunity of 80% is likely for adults <65yrs old for at least 5 months.  Several smaller studies have suggested even high levels of protection for longer periods of time.  For modeling purposes, we assume that at least 60% protection is possible for 12 months.  This model suggests that some 5M of the 90M Americans’ natural immunity is now too weak to protect them much.  This group has also lost members because many of them have acquired vaccine immunity. 

Behavior immunity helps to slow the spread of the disease (light blue part of graph above).  Countries such as Taiwan and Vietnam have successfully used only behavior immunity to keep the SARS-CoV-2 at bay for well over a year.  If everyone had masked, socially distanced, and followed all the other public health recommendations of the CDC, the USA would have reached effective human immunity sooner and avoided the fourth surge altogether.  But too many states relaxed mitigation measures too soon after January.  Fortunately, the pace of vaccination doubled from President Biden’s original goal of 100M shots in 100 days to 200M shots and compensated for this rapid relaxation.  We believe that the USA may be reaching effective human immunity soon.  Thousands of new cases will continue to be reported every day but the ability of the virus to spread exponentially will have been curtailed. 

It may be too soon to celebrate because this effective human immunity is soft and require at least 60M Americans to continue to follow public health guidance rigorously.  Over time, this soft human immunity will harden as vaccine immunity grows, even if at a slower pace than April due to vaccine hesitancy. New and more dangerous variants can still emerge and endanger this optimistic forecast, especially if international travel is relaxed too soon while the number of daily cases globally is still rising from surges in India, Brazil, and Turkey.   

Why Are So Many Seniors in FL Still Getting COVID-19?

Covid-19 mRNA vaccines work very well in real life.  But as more data are analyzed it appears that certain groups of people such as seniors (65+) do not benefit as much from the vaccine. 

We have been tracking the vaccine’s real-life efficacy through Florida’s Seniors First program to vaccinate everyone over 65 years old first.  As of April 19th, 3.6M seniors or 80% have been vaccinated with 2.9M (64%) completing the two-dose regime.  The pace of senior vaccinations has slowed recently and this may be linked to the plateau and now rise in relative infection for seniors (see figure below). 

There are several possible explanations for this observed phenomenon:

1.     Vaccine hesitancy expressed by 27% of Americans in recent polling,  Note that 80% of Florida seniors have already gotten their shot so polling answers may be more political posturing rather than reality.  Nevertheless, at some point before 100%, we will reach seniors who resist the vaccine, and improvement in relative infectious of seniors will end. 

2.     Weaker vaccine protection for seniors.  While mRNA vaccines are near 95% effective and people who are fully vaccinated have only a 5% chance of getting COVID-19 on average, people over 65 are less protected and may have as high as 39% chance of getting infected – near 8 times higher than average.  JnJ vaccine provides less protection for everyone.  Seniors typically have more comorbidities such as weakened immune systems and this may be one reason for their weaker protection.  As the rest of the state and country get vaccinated relative infection rates for seniors could increase more. 

3.     Premature relaxation of precautions after vaccination, especially in the 65-74 yrs old that are mobile.  Those vaccinated who drop masking and social distancing (which combined may be 90% effective) could reduce their overall protection against the virus.

4.     Vaccine effectiveness is believed to be 90% after 6-mo in general for mRNA vaccines, but this may not be true for seniors who may have shorter protection.  Seniors may require more frequent booster shots. 

5.     New and more contagious variants spreading now though Florida are not believed to escape mRNA vaccine clutches, but current vaccines may provide less protection against the new variants and may need to be re-tuned.

All of these factors suggest that it would be prudent for seniors to continue to follow good public health advise for masking, social distancing, and travel.  International travel to 80% of the world is discouraged by the US state department especially with the pandemic raging to record highs globally led by surges in India, Brazil, Turkey, and other hotspots around the world.

Vaccine Progress in Florida and the USA

The good news is that there are now 3 approved COVID-19 vaccines in the USA with more than enough doses to allow all American adults to be vaccine eligible by May 1st.  Two of the vaccines, Moderna and Pfizer-BioNTech, have already proven to be very effective in the field.  These are two-dose vaccines that can take 6 weeks to achieve full protection.  One way to track real-life efficacy is through Florida’s Seniors First program to vaccinate everyone over 65 first.  As of March 13th, 2.93M seniors or 65% have been vaccinated with 1.75M (39%) completing the two-dose regime.  If the vaccine is effective, the number of daily cases, hospitalizations, and deaths should all come down. 

The graph below tracks the relative susceptibility of Floridians by age to SARS-CoV-2 infections.  Seniors have always been more careful to mask-up and social distance since the first COVID-19 cases appeared in Florida and killed hundreds of seniors last spring.  Moreover, the oldest seniors (85+) have been the least mobile and thus least likely to spread the virus.  After rising slightly post year-end holiday gatherings that increased community transmission, relative infection rate (i.e. number of cases per capital for the age group divided by the number of cases per capita for the whole population) has steadily declined over the last 4 weeks from mid-February to mid-March for all seniors.  We are forecasting that these relative infection rates will continue to decline steadily for another 4 weeks as the number of fully vaccinated seniors approach 3.2M or 70% of the group population. After that, we believe that the rate of decline will slow and will run up against a stubborn core group of people refusing vaccines (estimated to be 27%)

This steady decline in senior susceptibility to COVID-19 will positively impact the overall case fatality rate (CFR = deaths/cases).  CFR has decreased from 2.5% in the first wave to 2.0% for the second wave to 1.5% for the third wave in FL.  We believe this will decrease below 1% soon as the median age of new cases falls further below the current value of 37 years old. 

This however does not mean that the virus will no longer be a threat.  The bad news is that the relative susceptibility of kids to SARS-CoV-2 has been increasing since school reopened in FL last year.  The trend appears to have worsened with the spread of the new and more contagious variants this year.  It could be several months before any vaccine is approved for kids under 16.  In the meantime, schools can reopen but it is important that teachers and staff get vaccinated, facilities get upgraded (e.g. ventilation), and masking and social distancing be enforced to mitigate the spread of the disease in schools. 

Herd Immunity vs Effective Human Immunity

Classic “herd immunity” is achieved when enough members of a population get infected and acquire natural immunity so that too few uninfected members are left to spread the disease.  The threshold percentage depends on how infectious the disease is and for COVID-19 it is not known but generally believed that 65%-75% of the population needs to develop immunity to stop this pandemic.  For humans, there are two more methods to slow or stop a pandemic: behavior immunity and vaccine immunity.  Governments can convince their citizens, or if necessary mandate, many public health policies that can mitigate the spread of disease.  Keeping your distance, wearing a mask, selective isolation, and improving personal hygiene are things that cattle can’t do but humans can and should do.  People in many countries such as Taiwan, New Zealand, Australia, and Vietnam have been able to control COVID-19 for over a year now without a vaccine or natural immunity.  Even in countries with greater emphasis on personal freedom vs community health, enough segments of the population do follow public health policies and contribute to the overall “effective human immunity” of the population. 

In the USA, behavior immunity has been unreliable but not totally useless.  When people see confirmed cases in the USA reach a horrendous 250,000 per day shortly after New Year more take notice and reach for their masks.  When they see 24M or 7.3% of their family and friends cumulatively get confirmed COVID-19 more may maintain social distance.  When the new administration mandated mask usage at Federal facilities it improves behavior immunity.  Near this level of infection, most people will have known at least someone within their immediate and one removed circle of family and friends that has had a confirmed case.  It is hard to maintain COVID denial when among their 10 closest friends and family and their 10 closest friends (100 people) someone they trust gets COVID-19.  Most people will modify their behavior – improving behavior immunity. 

Moreover, the true level of community infection could be 2 (2.8 is our best guess for USA cumulative to date) to 8 times higher than that reported as many people get asymptomatic and mildly symptomatic COVID-19 that never got tested and confirmed.  Everyone who gets COVID-19 develops certain amount of natural immunity depending on the severity of their case.  Currently the small number of reinfection, ~50 worldwide out of 111M confirmed cases and certain specific studies suggest that natural immunity could be better than 95%.  Adopting more optimal strategies of postponing or only giving one-shot vaccines to those who have had COVID-19 or postponing the second shot will allow us to reach effective human immunity sooner.  Some have suggested that when the cumulative confirmed cases pass 11%, the true level of natural immunity in the community could surpass the 70% needed for COVID-19 herd immunity.  This level was approached (9%) in North Dakota (ND) and South Dakota (SD) by Nov 15th  and Nov 27th, respectively, and daily case counts peaked then.  However, the fact that new cases continue to be reported every day in ND even as 13% of the population has now confirmed COVID suggests that the true level of total cases is not 6.5 times reported but much lower.  Looking at highly infected communities such as Miami-Dade County in FL where 14.5% of the population has had confirmed COVID-19, antibody tests (a convenient but possibly incomplete measure of immunity) show only a 22% cumulative positivity rate, and cases have peaked but not stopped suggesting that the level of hidden cases is probably only 2 times confirmed. 

Nevertheless, we may be closer to achieving effective human immunity than most are forecasting.  In ND, a combination of vaccine (currently 15% at least 1 shot) and natural (currently confirmed 13% and estimated total 35%) immunity could soon end the pandemic even though only 15% of their population is estimated to adhere to CDC guidance for masks and social distancing.  Similarly in Miami-Dade, effective human immunity is approaching 70% (n37%+v10%+b18%).  For the USA as a whole, 8.6%-25% natural immunity currently plus 13% vaccine immunity and 25% behavior immunity may allow the country to achieve effective human immunity by the end of April (n29%+v26%+ b20% – see graph below). 

This optimistic view may be undercut by communities rushing to reopen and removing mitigation measures before the contagion has fallen below critical levels.  The other caveat is that if the more contagious variants take hold in the USA, another surge in cases may occur stretching out the time to effective human immunity.  Even under these more pessimistic scenarios, the USA should achieve effective human immunity by mid-summer if vaccinations proceed at the current 25M people per month.    

Re-opening Schools

The new US administration has made re-opening schools a priority.  There are many benefits to re-opening schools and certainly, re-opening schools are more important than re-opening bars and many other businesses.  But there are many risks as well. 

One of the risks is the susceptibility of kids to COVID-19.  Kids suffer far fewer fatalities and hospitalizations than older adults (although kids could suffer long term ill effects with COVID-19).  The question really comes down to how easily do kids acquire the virus and how easily do they transmit COVID-19 to others and fuel the pandemic. 


 In Florida, most schools and universities reopened in late August 2020.  Since then the number of daily confirmed cases per capita has risen steadily for all age groups.  College and university-aged (18-24yrs) students are most active and mobile and show the highest cases per capita – currently 30% above average.  High school students (14-17yrs old) have always tracked near the average infection rate.  Elementary school student (5-10yrs old) infection started out near 30% to 40% of average but has risen steadily over the last 5 months.  Currently, they are 64% as contagious as the average Floridian, and middle school students are 81% as contagious (see graph below).

 Why have kids become more contagious? 

1.     One explanation is that with school reopening, kids are tested more often.  While testing has increased, the positivity rate has gone up as well reflecting a real increase in community spread.  Over the last 7 weeks, tests have topped out at 100k/day in FL. 

2.     The spread of more contagious variants from the UK, South Africa, and Brazil has increased the rate of transmission, including among kids.  Whether kids are more susceptible is an open question.  FL data suggest that kids may be. 

 Re-opening schools should be done in phases with K-5 grades re-opening first and perhaps high schools not at all until community spread is much lower than it is today.  In Florida, most high schools have re-opened along with most sports and this has exacerbated outbreaks in Florida.  We strongly discourage high contact sports such as high school wrestling that have led to super-spreader events. 

Trump’s Legacy – Half a Million Americans Die of Covid-19

Before noon on January 20th, President Trump will leave his office.  At that time the reported death toll from COVID-19 in the USA will be over 400,000 – the exact number depending on who does the tallying.  Worldmeter will show 412k – real-time, Johns Hopkins will show 402k – lagging by a day, and CDC will show lower – lagging by a couple of days.  All these estimates understate the real toll history will attribute to Trump – over 500k Americans died on his watch.    

COVID-19 death reporting has time lags and other issues.

1.     Accurately assigning the correct cause of death is sometimes more art than science.  There are the underlying cause and the proximate cause issue.  Sometimes COVID-19 starts a chain of events that lead to death many months later from lung, heart, kidney, liver, or diabetes problems that are not uniquely attributable to COVID-19.  The US CDC separately defines confirmed and probable counts and reports both now.  A confirmed case or death is defined by matching confirmatory laboratory evidence for COVID-19.  A probably case is more loosely defined but is now included by most states reporting to the CDC.  There is no time limitation.  (Other countries use different definitions that sometimes make comparisons across jurisdictions difficult.)

2.     Excess deaths, or deaths above normal average year expectations, often exceed the reported COVID-19 deaths implying that undercounting of COVID-19 deaths may be occurring using the direct method.  As of Oct. 15th when reported deaths were 216k, CDC estimated excess death near 299k – 42% more.  

3.     Reported deaths sometimes occur more than a month after the actual date of death  Currently, 60% of all US deaths are reported within 10 days of death but some state (like Florida) and many countries can take more than 2 months to be just 75% complete.   

Our models for the COVID-19 virus infection and death are based on curves that rise quickly after exposure, peak, and then fall off with a long exponential tail.  The virus incubates in the victim’s body and proliferates until 10 days after exposure when the viral load begins to decline in response to the body’s defenses.  Those with a low overall viral load may never see a high enough load to experience any symptoms or request testing.  About 10% of those exposed and get tested, typically around day 5, test positive (the current US weekly positivity rate).  About half of these never develop any symptoms but carry a high enough viral load to infect others for about 10 days after test or 15 days after exposure.  Half of those who test positive will usually experience some symptoms.  Most will stay home and treat themselves with medical guidance.  Some 6% of all positives will get sick enough to go to the hospital – although this has dropped recently to near 3%.  The steady drop since August is due to more kids and young adults being positive not requiring hospitalization, but it could also be due to overcrowding of hospital systems in certain regions like Los Angeles and Arizona.  About 1.5% of all those that tested positive will ultimately die in an average of 14 days from testing and 19 days from exposure.  As noted above, these deaths could take up to 8 weeks to get reported and counted.    

Thus when President Biden is sworn in on Jan 20th there will be:

1.     Deaths that have already occurred before Jan 20th that will get reported over the following 8 weeks (35k). 

2.     There will be a percentage of the 3.4M cases confirmed in the period before Jan 20th that will progress to hospitalizations, ICUs, and deaths that no one will be able to save.  The full accounting will take another eight weeks (69k).

3.     Alternatively, by the end of March the excess death report from the CDC will provide a measure of all deaths to Jan 20th and a portion of deaths to Feb 3rd that should be attributed to Trump’s policies and actions that President Biden could not reverse (140k). 

Whether using the case classification method or the excess death certificate method – the conclusion will be that more than half a million Americans died of COVID-19 under Trump’s watch that no one else could have saved.  Some might argue that every country suffered from the same devastating COVID-19 pandemic – it’s not Trump’s fault.  However, if Trump performed as well as the average government around the world and experienced the same average fatality per capita, only 71k Americans would have died by Jan 20th.  Trump’s gross mismanagement of the pandemic will be a large part of his legacy. 

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