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Covid Immunity - By Spencer Kroll MD PhD

part 1

Many people are wondering about their immunity status to the COVID-19 virus.  This is either after natural infection and recovery.  Or alternatively after vaccination.  In some cases, people have been infected and then vaccinated.  And in some cases, people have had "breakthrough" infections after vaccination.

There is tremendous confusion and false messaging about testing and its implications for evaluating immunity.  This has impacted peoples moves towards vaccination and "booster" shots.  It has also impacted people's general behavior regarding quarantine, masking and testing.  

Here are the latest facts, presented from the latest scientific information, rather than spin from opposing media outlets.

1) The mRNA vaccines are effective in keeping people out of the hospital and dying.  This immunity - both in terms of antibody based immunity as well as longer term T cell and memory B cell immunity has shown some fall off over time.  It has also shown some limitation in terms of response to Delta variant virus.  

2) The mRNA vaccines may not provide the same adaptable immunity as infection.  This means that vaccines, which are designed based on the Corona virus spike protein, may not be as effective as getting infected, as the virus spike protein changes through emerging variants.  

3) Getting infected, and the natural immunity that should follow is not a viable option as a therapeutic strategy to control the virus.  This strategy has not worked in any country or location where it has been tried.  There is HIGHLY variable response in terms of immunity to infection.  Some people with mild infection develop early slight neutralizing antibodies that dissipate over weeks.  This is similar to the immunity that develops from other types of corona viruses that are endemic and cause colds and mild upper respiratory infections.  People with more severe cases have little antibody early in the infection and develop a "cytokine storm" and vigorous antibody production as they get significantly sicker.  These people usually require hospitalization and sometimes intubation.  People should not bet on where they will come out regarding this because a milder infection causes less sustained neutralizing antibodies to fight future encounters with the virus.   Neutralizing antibody production after infection lasts for a shorter duration than vaccination. 

4) Children may be partially protected from infection because other corona viruses are endemic in pediatric patients.  This is very important to testing because antibody testing cross reacts with antibodies to these other corona viruses and may provide a false positive result in both adults and children.  

5) Natural infection, according the latest studies from Israel and complementary ones from other countries, followed by 1 dose of mRNA vaccine may provide the best protection from delta variant - which now makes up 99% of the infections in the United States.  This result does not undermine the effectiveness of two doses of the mRNA vaccine:  which is a predictable result.  The limitations of vaccination in this regard need better global understanding.   

6) Immunity testing has also been very misunderstood.  Before the late summer, commercial laboratories were testing a polyclonal mix of antibodies to corona virus and reporting a qualitative result - either positive or negative.  There are multiple antibodies that can be measured for Covid19 including multiple spike domains, the receptor binding domain and nucleocapsid domain.  These different measures have vastly different results for interpretation of immunity from infection versus immunization.  Most doctors DO NOT understand these distinctions, nor are they clear on the results sheets delivered from the commercial laboratories.  In many instances, results that showed immunity may have shown immunity from infection - NOT from vaccination.  Conversely, negative results from commercial laboratories may have been because the incorrect antibody tests were being ordered.  

7) In August, 2021, the commercial laboratories began to differentiate testing of different Covid19 antibodies and reporting quantitative values.  First off, these quantitative values, according to most experts should not be interpreted as the strength of immunity or compared between samples of laboratories.  People are going for repeated antibody levels and there is validity to these numbers besides whether they are positive or negative in terms of protection, or to the strength of protection.  There MAY be correlation , however, to a projection of the timing of falloff of immunity if the numbers are dropping.  

8) The CDC is not recommending serology (antibody testing) and has only issued emergency use authorization of these tests.   They specify that there is "currently no recognized public health or clinical indication for preferential use of semi-quantitative tests.

9) Longitudinal patient follow-up studies are ongoing to measure antibody levels before and after vaccination or natural infection to identify an association between responses below a certain threshold and vaccine failure or re-infection. These longitudinal patient follow-up studies are expected to elucidate the relationship between antibodies and protection from reinfection. In addition, T-cell-mediated adaptive immunity following natural infection, which is much more difficult to measure, likely contributes to protection from subsequent exposure to the virus.

10) Manufactured antibody infusion therapy (i.e. Regeneron or Eli Lilly), will affect accuracy of antibody detection for months until these external antibodies are cleared by the body.  These therapies are for short term therapy and not for long term immunity.  

In Part 2, I will discuss the differences between antibody tests in terms of which ones to utilize, accuracy and reproducibility.  


As a concierge doctor, he practices evidence-based and integrative medicine. Focusing on the use of a variety of treatment modalities for his patients. As a patient in our practice, you will be part of our family and as such we will strive to treat you like one!

Please call us at 732-591-8840 to schedule your appointment. Learn more about all the Concierge Medicine that we offer.

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KrollMD exists to provide a unique patient experience. Dr, Kroll and his staff address all aspects of our patient’s needs. Ranging from the time they walk into our office to the time they leave and far after. Our comprehensive, patient-driven practice allows us to get to know our patients better. Knowing them on a personal level to deliver bespoken medical care. Concierge medical care which surpasses our patients’ expectations.


At KrollMD we provide a full range of diagnostic testing. Along with the best treatments all under one roof. As a patient, you will no longer go to multiple different centers and specialists. We’re equipped with the latest diagnostic equipment. Some samples of our testing capabilities include:

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At KrollMD, we are grateful for our patients. Many of them have taken the time to share their experiences with our Dr. Kroll and our staff. Sharing on the web via social media outlets and review sites.   We’re honored and proud to have received such acclaim from our patients. Our staff and family doctor feel humbled and grateful for these kind words. We look forward to caring for you and your family!

Author: Spencer Kroll MD PhD FNLA

Board Certified in Internal Medicine and Specialist in Concierge Medicine & Executive Health. Dr. Kroll practices Internal Medicine and Integrative Medicine with focus on preventative medicine.  Dr. Kroll is also board certified by the American College of Lipidology and is a Fellow the National Lipid Association/American Board of Clinicial Lipidology.  In addition, Dr. Kroll holds a doctorate degree in Clinical Pharmacology and Molecular Biology.  Dr. Kroll has been a medical instructor at Georgetown University and is currently a clinical instructor for University of Southern California.  Dr. Spencer Kroll received his bachelor of sciences from the Cornell University in Biology. He obtained his Masters Degree and PhD from CUNY/Mount Sinai School of Medicine.  He received his Medical Degree from George Washington University. He completed his medical residency at Georgetown University. Dr. Kroll has been practicing in Marlboro New Jersey for more than 20 years.  He has received numerous awards and recognition as a top doctor in his field.

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