Written by Paul E. Alexander, PhD; Howard Tenenbaum, DDS, PhD; and Parvez Dara, MBA, MD.
We have looked at the published evidence and can conclude based on the existing body of evidence, that reinfections are very rare, if at all, and based on typically one or two instances with questionable confirmation of an actual case of re-infection e.g. flawed PCR testing etc. (references 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23).
Importantly, the World Health Organization (WHO) has recently (May 10th 2021 Scientific brief, WHO/2019-nCoV/Sci_Brief/Natural_immunity/2021.1) alluded to what has been clear for many months, which is that people are very rarely re-infected. The WHO is very late but, hey, better late than never. The key points they have stated in this briefing that stand out and warrant a mention (again, we always knew this and tried informing the CDC and WHO of this over the last year) include the following:
i) Within 4 weeks following infection, 90-99% of individuals infected with the SARS-CoV-2 virus develop detectable neutralizing antibodies.
ii) Available scientific data suggests that in most people immune responses remain robust and protective against reinfection for at least 6-8 months after infection (the longest follow up with strong scientific evidence is currently approximately 8 months).
iii) Studies aimed to detect immunological memory including the assessment of cellular immunity by testing for the presence of memory B cells, and CD4+ and CD8+ T cells, observed robust immunity at 6 months post-infection in 95% of subjects under study, which included individuals with asymptomatic, mild, moderate and severe infections.
iv) Current evidence points to most individuals developing strong protective immune responses following natural infection with SARS-CoV-2.
We also wish to re-iterate the accumulated strong evidence that prior infection with other coronaviruses and common cold coronaviruses confer cellular immunity via T-cell immunity etc. (Weiskopf, Grifoni, Le Bert, Mateus, Tavukcuoglu, Cassaniti, Dykema, Echeverría, Bonifacius) (references 1, 2, 3, 4, 5, 6, 7, 8, 9). Indeed, the evidence now abounds that SARS-CoV-2-reactive CD4+ T cells as an example, are seen in unexposed individuals, suggesting preexisting cross-reactive T cell memory. “A positive response was observed up to 12 months after COVID-19 infection (median 246 days after symptom onset; range 118-362 days)… long-term SARS-CoV-2 T-cell response might accompany a waning humoral response”. Of note, SARS-CoV-2 T-cell response seems to be mainly mediated by CD4 T cells. This immunity appears also to be long-lasting e.g. SARS-1 has remained for 18 years. Of 23 patients who had SARS-1 in 2003, researchers found all 23 retained memory T cells induced by the parental SARS-1 pathogen in their systems after 17 to 18 years. Moreover, when they looked at convalescent SARS-CoV-2 patients (n=36), they uncovered that the 36 had also produced similar memory T cells.
In closing, we also argue that if you are re-infected, it is most likely not with the initial parental strain you were infected with and most likely with a variant. Moreover, had you developed natural exposure immunity, this is usually a robust and durable safeguard against variants. There are many questions at this time as to the ability of the very narrow ‘spike-specific’ immunity (spike epitopes) conferred by the mRNA and adenovirus vector delivery platforms. It is possible and highly probable that variants could blow past the existing vaccines, and we are seeing this today whereby doctors report that 60% of the new COVID infections already have had both vaccination shots. This phenomenon post-vaccination warrants urgent focus by authorities and study.
Paul Alexander holds a masters of science degree in epidemiology and community health from the University of Toronto, a masters of science degree in evidence-based medicine from Oxford University, masters schooling in Health Sciences also at York University, Toronto, and a PhD in evidence-based medicine and research methods from McMasters University, Hamilton. He currently holds a post as Assistant Professor at McMaster’s University in the HEI Research Methods department and completed his doctoral research and post-doctoral work under the founder of Evidence-based medicine (EBM), Dr. Gordon Guyatt. He served in the Trump Administration as a senior COVID-19 advisor for the Assistant Secretary of Health and Human Services and also worked for WHO and the Pan-American Health Organization in Washington, D.C. from February 2020 onwards as a COVID-19 consultant for research methods and related matters. He also worked for the WHO/PAHO prior to the onset of the pandemic in developing evidence-based tools for low- and middle-income nations.
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