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.   

 

Comments

Post a Comment

Popular posts from this blog

Could Florida be the Next Epicenter in the COVID-19 Pandemic?

Image
Florida Governor DeSantis has failed to recognize the seriousness of the exploding Covid-19 Pandemic in Florida.   His slow response and poor judgment have already cost many Floridians their lives and may cost many thousands more if he fails to act now.   State Infections/M Infections Deaths Mortality Mortality Coincident Lagged5 NY            2,361 45934 604 1.3% 3.6% NJ               994 8825 108 1.2% 5.1% LA               591 2746 119 4.3% 12.7% WA               486 3700 175 4.7% 8.8% MA               466 3240 35 1.1% 5.1% MI               366 3657 92 2.5% 8.4% CT               362 1291 27 2.1% 8.2% CO                  301 1734 31 1.8% 5.3% IL       
Read more

COVID-19 Infection and Mortality Rates as a Function of Age and Gender

Image
With over 2.4 million COVID-19 cases and over 160,000 deaths globally, there is a lot of data that can be analyzed to better understand this virus as a function of age, co-morbidities, medical history (such as prior exposure to coronaviruses like SARS, and other vaccines like BCG), etc.   The two important factors that have been noted since the early days of this pandemic are age and gender and they continue to be the most important factors.   We look at the age and gender dependencies with the best single data set provided by the Spanish Health Department containing over 200,000 cases (or 0.4% of the total population) and over 20,000 deaths.   Spain has tested over 2.0% of its population which while short of a comprehensive sample does begin to give us some ideas about how the disease has affected the entire country.   We look at the probability of a random person acquiring the disease as a function of age.   We know that this sample is not truly random nor comprehensive but it d
Read more

Pre-Thanksgiving Dip in COVID-19 Cases

Image
COVID-19 cases in the USA have shown a sharp decrease over the last 8 days causing the 7-day rolling average to peak and rollover (see figure below – red squares).   The question is whether this is measuring a real lasting phenomenon – perhaps attributable to local COVID-19 fires burning out, or to mitigation factors taking hold, or to some temporary factor associated with the Thanksgiving holiday.   The answer is probably a combination of all three that will ultimately be overwhelmed by an increase in Thanksgiving transmission. Some COVID-19 outbreaks have burned so strongly and for so long (3-4 months) that local “herd immunity” may be acting as a retardant to the fire.   For example, in North Dakota (ND) 10.3% of the population has now been confirmed infected (see table below).   State Confirmed Testing Est. Pop Deaths Death per Fatality   Infection % Positive % Infection %
Read more