Nevertheless, a few months following the second Pfizer vaccine shot, spike-specific antibodies were further enhanced by a third mRNA injection and/or new infections caused by the SARS-CoV-2 variant [30]. levels of IgG4 in people who were administered two or more injections of the mRNA vaccines. HIV, Malaria, and Pertussis vaccines have also been reported to induce higher-than-normal IgG4 synthesis. Overall, there are three critical factors determining the class switch to IgG4 antibodies: excessive antigen concentration, repeated vaccination, and the type of vaccine used. It has been suggested that an increase in IgG4 levels could have a protecting role by preventing immune over-activation, similar to that occurring during successful allergen-specific immunotherapy by inhibiting IgE-induced effects. However, emerging evidence suggests that the reported increase in IgG4 levels detected after repeated vaccination with the mRNA vaccines may not be a protective mechanism; rather, it constitutes an immune tolerance mechanism to the spike protein that could promote unopposed SARS-CoV2 contamination and replication by suppressing natural antiviral responses. Increased IgG4 synthesis due to repeated mRNA vaccination with high antigen concentrations may also cause autoimmune diseases, and promote cancer growth and autoimmune myocarditis in susceptible individuals. Keywords:IgG4 antibodies, mRNA vaccines, immuno-tolerance, auto-immunity, SARS-CoV-2, COVID-19 == 1. Introduction == In a relatively short period after the beginning of the COVID-19 pandemic, two mRNA vaccines, BNT162b2 (Pfizer-BioNTech, New York, NY, USA) and mRNA-1273 (Moderna, Cambridge, MA, USA), were granted the first-ever emergency use authorization. These mRNA vaccines represented a new type of vaccine that comprises synthetic mRNA molecules that contain the coding sequence necessary to build the SARS-CoV-2 Spike protein, which is usually encased in the lipid nanoparticles (LNPs) to allow for the delivery of mRNA to cells. The main characteristic of the mRNA vaccine platform is that the proteins are synthesized within the host cells, mimicking a natural contamination with SARS-CoV-2 [1]. Contemporary investigations have contrasted the seriousness of symptoms in COVID-19 individuals infected with the SARS-CoV-2 Alpha, Delta, and Omicron variants, as well as the effectiveness of mRNA immunizations versus each variant among individuals admitted to hospitals in the United States from March 2021 to January 2022. COVID-19 vaccines were discovered to be quite efficient (90%) in avoiding intensive care unit (ICU) admissions caused by Alpha, Delta, and Omicron variants. However, three vaccine injections were needed to give protection against the Omicron variant, whereas two injections sufficiently safeguarded against the Alpha and Delta variants [2]. When people were admitted to hospitals, the Omicron variant was linked to fewer clinical adverse outcomes than the Delta variant. Despite that, ALK inhibitor 2 the Omicron variant still produced considerable clinical symptoms and mortality [2,3,4,5,6]. It is worth ALK inhibitor 2 noting that there are conflicting pieces of information about the level of protection offered by these vaccines. Although the Center for Disease Control (CDC) in the United States has stated that throughout the pandemic, mortality rates have been higher in the unvaccinated than Itgb1 in the vaccinated [7], the data in the United Kingdom contradict the CDCs findings. Specifically, the Office for National Statistics (ONS) in the United Kingdom has reported that from April to mid-November 2021, deaths in unvaccinated people were higher in comparison with vaccinated people who had received a second vaccine dose. However, from the end of November 2021 to December 2022, this situation reverted: deaths were higher in vaccinated people who received a third vaccine dose compared with the unvaccinated [8]. Moreover, a recent work investigated a probable relationship between COVID-19 vaccination uptake in Europe in 2021 and monthly extra all-cause mortality in 2022; that is, mortality was higher than before the pandemic. All-cause mortality during the first 9 months of 2022 increased more in countries with higher 2021 vaccination uptake, according to analyses of 31 countries estimated by populace size; a one percentage point increase in 2021 vaccination uptake was associated with a monthly ALK inhibitor 2 mortality increase in 2022 of 0.105% (95% CI, 0.0750.134). The relationship remained strong after adjusting for alternative factors [9]. Although they can induce significant neutralizing anti-spike IgG and IgA responses, all three anti-COVID-19 vaccines: Pfizer, ALK inhibitor 2 Moderna, and Astra Zeneca ChAdOx1, (Cambridge, UK) appeared to be only transiently protective against SARS-CoV-2 contamination and transmission [10,11,12,13]. The high rate of breakthrough infections brought on by the Omicron variant suggests that the sterilizing protection offered by the existing immunization schedules is usually minimal [14]. There are several evasion strategies that SARS-CoV-2 uses to elude immunological monitoring and attack,.