Is Herd Immunity Possible for COVID-19?

Jia-Yia Liu, MD
Board Certified Infectious Diseases and Internal Medicine
Loma Linda University School of Medicine, Assistant Professor
Cedars-Sinai Medical Center Attending Medical Staff
AMPSAA President

Herd immunity has been an effective solution to eradicate devastating global infections. Vaccination is the modern herd immunity and has been successful globally. The benefits of vaccinating a population to end the chain of transmission for contagious infections are successfully illustrated in the 99% reduction of cases of invasive Hemophilus influenza type B in children to also the eradication of smallpox from the world by 1979.[1,2]

Our current pandemic has unified the academic world, flooded an incredible amount of funds into vaccine development in an unbelievable race against time. Unfortunately, currently there is no effective and safe vaccine. Projections from expert infectious disease scientists do not predict we will have an effective and safe vaccine until sometime in 2021.

Even when a COVID-19 vaccine is available, is herd immunity achievable? Different diseases have different herd immunity thresholds, or the percentage of immunized people who can no longer transmit disease. The highest threshold is measles at 95%, while the lowest threshold is H1N1 influenza at 25%. The SARS-CoV-2 herd immunity threshold is predicted to be 50-67%.[3]

The science of SARS-CoV-2 immunity is still under discovery. The human immune system is a complex and intricate yet delicate array of protein signaling and cellular recruitment, including adaptive and innate immunity and complement cascades. In addition, thousands of enzymes, cofactors, lipids and other proteins delicately regulate the homeostasis required for optimal cellular health. The wrong signals can cause devastating results to the person and illicit auto-destruction, such as in autoimmune diseases, septic shock and cytokine storm in COVID-19, or cause chronic symptoms such as fatigue, brain fog, pain, diarrhea, bloating, shortness of breath and depression.

Asymptomatic and pre-symptomatic infections are the drivers of transmission as unknowingly people have their cells transformed into viral factories generating millions of viral progenies eager to infect another victim. In the microbial world, time is of the essence, as each human cell can yield several thousand viral progenies.[4] In SARS-CoV-2, the period of maximum contagiousness is 24-48 hours before the appearance of symptoms. [5] As little as 15 nonconsecutive minutes in close proximity to a silent carrier can transmit SARS-CoV-2 to another.[6] In addition, airborne transmission, although not the primary mechanism, occurs.[7] A vaccine gives hope to prevent viral replication and end this chain of transmission.

Achieving herd immunity through natural SARS-CoV-2 infection appears to have been Sweden’s unofficial policy in the beginning of the pandemic. Sweden, with a death rate similar to Italy, also had the highest death rate of all the Scandinavian countries. As the pandemic continued, Sweden began to implement policies to mitigate transmission including closing some schools and modifying hours and occupancies for businesses.[8,9] It is estimated that only 6-8% of Sweden’s residents had antibodies against SARS-CoV-2 by June 2020.[10]

For COVID-19, achieving 50% immunity, via wild-type infection or vaccination, is challenging for several reasons. First, the adaptive immune response seems inadequate for protection. SARS-CoV-2 antibodies appear to wane at 3 months, while others never mount a humoral response, regardless of severity of disease.[11,12,13,14,15] Convalescent plasma and monoclonal antibodies have not been shown to be effective at treating COVID-19 patients.[16,17] Second, reinfection has been proven to occur in SARS-CoV-2.[18,19] Yet all hope is not lost, as there is evidence T-cell immunity may persist despite the lack of IgG response.[20]

The reality is, not everyone who is exposed to SARS-CoV-2 become carriers or develop COVID-19, even amongst families living together. Protection from SARS-CoV-2 may be primarily from the innate and complement immune systems. Defense by our epithelial cells lining our skin, gastrointestinal tract and our respiratory tract, the composition of the mucus secreting defensins or antimicrobial peptides and the complement cascade and other protein signaling, may determine whether an infectious virus will be successful invading and hijacking our cells. Do some have more competent cells in their epithelial layer, more defensins in their mucus, and more efficient phagocytosis and complement systems? If so, could something in their diet and lifestyle be contributing to their elite immune system function? We know there is strong evidence that poor diets and lifestyle promote chronic diseases such as obesity, diabetes, cardiovascular diseases and cancers, which in turn elevates infection risks including COVID-19. Mounting evidence have shown vitamin D deficiency and zinc deficiency correlate with poorer COVID-19 outcomes. [21, 22,23,24,25] Evidence of micronutrient deficiencies causing other diseases is well documented. (Table 1) Could Americans be chronically suffering from subclinical nutrient deficiencies that are amplified by COVID-19?[26]

Reference for Table 1. https://ods.od.nih.gov/factsheets/list-all/

The path to economic recovery and freedom of mobility is being falsely placed on the hopes of vaccination. In reality, like the human body, the solution to this pandemic is multifaceted. Transmission needs to be mitigated internally and externally today, not on the hopes of tomorrow. To reduce the risk of a poor outcome each individual has the power to optimize his/her cellular function through a diet rich in essential micronutrients, anti-oxidants and anti-inflammatory foods and strive to exercise and obtain quality sleep. We need not look any further than Blue Zone communities around the world who have the highest rate of active centenarians as examples of the power of lifestyle, diet and exercise.[27] In addition, proper use of protective masks and frequent, affordable, rapid, home saliva tests with same day, if not same hour results, need to be made available to all Americans.[28,29,30,31] Several American college campuses including University of Illinois, Urbana-Champaign, with a 7day positivity rate of 0.24% as of October 26, 2020, have successfully demonstrated frequent rapid testing and universal masking works.[32]

While we await for society to give us better tools to diagnose, treat and prevent COVID-19, we can draw upon our biochemistry and physics backgrounds and empower our patients to strive for healthier lifestyles, now, to protect themselves internally and externally to change the trajectory of this pandemic and the rate of other chronic illnesses in America.

REFERENCES

1.https://www.cdc.gov/vaccines/vpd/hib/public/index.html#:~:text=Every%20year%20about%2020%2C000%20young,children%20in%20the%20United%20States
2.https://www.who.int/news/item/13-12-2019-who-commemorates-the-40th-anniversary-of-smallpox-eradication
3.https://jamanetwork.com/journals/jama/fullarticle/2772167
4.https://www.ncbi.nlm.nih.gov/books/NBK8181/#:~:text=The%20reproductive%20cycle%20of%20viruses,to%20several%20thousand%20poxvirus%20particles
5.https://www.nature.com/articles/s41591-020-0869-5
6.https://www.statnews.com/2020/10/21/cumulative-time-covid-19-spread/?fbclid=IwAR0khmUMAk-vTMF-3m9hhwLF4Z-2FzIkLP9HbexEMvsgwUymYxWECMzAd-w
7.https://jamanetwork.com/journals/jama/fullarticle/2768396?fbclid=IwAR1pMWwcZy1qODYLScxPpe4275ZmEtA7jK9p-krQyQPDOosFCjbfT8r8zy0
8.https://www.nytimes.com/2020/07/07/business/sweden-economy-coronavirus
9.https://www.medpagetoday.com/infectiousdisease/covid19/87812?fbclid=IwAR0CzIsf9lL6q1zMCnUmG95V1degKVSgYnBHC3PMTqdZ5zL3Tfmcn7gVpbU
10.https://www.sciencemag.org/news/2020/10/it-s-been-so-so-surreal-critics-sweden-s-lax-pandemic-policies-face-fierce-backlash
11.https://www.nejm.org/doi/full/10.1056/NEJMoa2026116?fbclid=IwAR3aH9Y2xAJZ7lQvh7g20N7BIG2fSfUP8Foem5_cUOF0ZtHC335aOFO_OD0
12.https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2769741
13.https://wwwnc.cdc.gov/eid/article/27/1/20-3772_article
14.https://wwwnc.cdc.gov/eid/article/27/1/20-3515_article
15.https://www.imperial.ac.uk/news/207333/coronavirus-antibody-prevalence-falling-england-react/
16.https://www.npr.org/sections/coronavirus-live-updates/2020/10/26/928072014/eli-lilly-ends-coronavirus-antibody-treatment-trial-other-studies-go-on
17.https://www.cidrap.umn.edu/news-perspective/2020/10/study-finds-no-covid-19-benefit-convalescent-plasma
18.https://www.medpagetoday.com/infectiousdisease/covid19/88234?fbclid=IwAR03se_ELazvYs3eSymWNOib86DOJ9dSRPeuCjon8G1thu0vWbVfyzRU0CE
19.https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30764-7/fulltext?fbclid=IwAR1ZmRIdim4H4ig3k65PKT8MwPE2Tr9myPEbATUmXWd60hLleAmtt-MUZg4
20.https://wwwnc.cdc.gov/eid/article/27/1/20-3772_article
21.https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2770157?fbclid=IwAR0Nhddk895vLIhORRXUFEl4lmMLOitdET7MnySZK4lMd56xb_DW1EjZnHs
22.https://www.thelancet.com/journals/landia/article/PIIS2213-8587(20)30268-0/fulltext?fbclid=IwAR2xgdsJ-W_ahxC9VgGE1Sxnb_4LmY-TjPg42SOmRfijcvV8oZ270XhKUZg
23.https://academic.oup.com/jcem/article/105/10/dgaa432/5867168
24.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7489890/
25.https://medicalxpress.com/news/2020-09-zinc-blood-death-patients-covid-.html?fbclid=IwAR2uaTJS2ycril4h_L26lOLJoFy3CufBwVhIrt7q66Cax_SAYP98ZGML2po
26.https://www.medscape.com/viewarticle/935666?fbclid=IwAR0INwn4pCDe2Ri_lBftJZpRTF5W5DdhInQsHw5rnsHs_EoZ5WwdVcJsBTA
27.https://www.bluezones.com/live-longer-better/#section-1
28.https://www.rapidtests.org/
29.https://www.medscape.com/viewarticle/935666?fbclid=IwAR0INwn4pCDe2Ri_lBftJZpRTF5W5DdhInQsHw5rnsHs_EoZ5WwdVcJsBTA
30.https://thehill.com/policy/healthcare/511513-study-shows-most-homemade-mask-help-slow-droplets?fbclid=IwAR2jOv_3jFBFWyeW16WgAnKRlkStOVpOki7xCZ07NAzNNn52kKKagNtnY0k
31.https://pubmed.ncbi.nlm.nih.gov/29140516/
32.https://www.statnews.com/2020/10/21/cumulative-time-covid-19-spread/?fbclid=IwAR0khmUMAk-vTMF-3m9hhwLF4Z-2FzIkLP9HbexEMvsgwUymYxWECMzAd-w