Specific
A recent paper by Yonker surveyed the biomarkers of vaccinated individuals, both with and without post-vaccination myocarditis. The main differentiator between the group with myocarditis and those without was the persistence of full length spike protein, unbound by antibodies[
3]. Given that this is the sole gene encoded by most of the vaccines and has multiple documented pathological mechanisms[
4], it is a likely aetiological factor in post-vaccination syndrome.
Cases of blood thrombosis after vaccination typically occur within one month of receiving the injection[
14,
15]. A test for spike protein contains two important quantities, the concentration of spike protein, as well as the time since vaccination. While most often after injection spike protein concentration drops off quickly after one week [
16], persistence of high levels of spike protein for months after injection has been documented in a subset of vaccinated individuals [
17]. It is unclear what the individual factors are affecting long-term spike protein levels; we propose a model for the long term persistence of spike protein.
The first factors are the variations in the initial dose of spike protein encoding mRNA, which can vary due to storage, dilution and administration. Once the mRNA is in the body, the level of spike is in competition between mRNA degradation and protein expression from the mRNA (
Figure 1). We also propose a third alternative between degradation and expression, that of conversion to a reservoir. Reverse transcription into the genome is possible [
18]. Additionally, a discovery of DNA contamination in a broad swathe of mRNA vaccine vials[
19], potentially opening the possibility of but microbiota transfection through the mechanism of horizontal gene transfer [
20].
While the half-life of RNA is well known, and endogenous mRNA has a half life of approximately 10 hours [
21], it is known that pseudouridinylated RNA is far more persistent[
22,
23], and less is known about the degradation of the N1-methyl-psuedouridnylated RNA used in the mRNA vaccines[
2]. Persistence of spike protein appears to be the factor which differentiates those with post-vaccination myocarditis vs vaccinated people without myocarditis[
3].
In interpreting the causes of interpersonal variation in vaccine response, we will restrict our analysis to disease etiologies tracing to the spike protein in the vaccines. While there may be other contributing factors, they are outside the scope of this review.
Variation in the dosing of the vaccine can greatly influence the response to the vaccine. It is observed that there was significant variation in the adverse event rate of different batches. Furthermore, the rates of AEs differed significantly depending on whether or not aspiration was performed. A strong relationship has also been shown between the dose of mRNA received and the rates of AEs, both when comparing brands (Moderna Covid-19 vaccine delivers a higher dose of mRNA than the Pfizer BNT162b2) and when comparing AE rates by total cumulative dose (i.e. comparing those receiving boosters with those receiving the initial series).
However, assuming the delivery is constant, there are still important sources of individual variation which can impact the vaccination response.
Viewing the series of events sequentially, the RNA must enter the cell, be read by the ribosome to express spike protein, after which it is degraded (in principle). Lacking an intact degradation pathway, the modified RNA will linger around and keep producing spike protein in principle. Minimal information is known about the biodegradation of modified mRNA in humans [
2].
The most important factor here is whether the injection was performed into the deltoid muscle, as intended, or some escaped into the bloodstream, which is largely set by the conditions of the injection itself (if aspiration was standard procedure). Still, individuals vary in their cellular affinity to take up extracellular RNA via endocytosis [
24,
25,
26]. While it is unclear of their relevance in this case, there are genetic variations in endocytic pathways [
27,
28]
It is possible that gross blood flow parameters, such as coagulability and blood pressure influence biodistribution. As hypercoagulation is an etiology behind vaccine injury[
29] and long covid[
30], genetic factors underlying coagulability may be associated with the prognosis of either condition. A Genome wide association study (GWAS) found that gene polymorphisms of proteins involved in coagulation were associated with acute Covid-19 prognosis[
31]. These include MBL2[
32], ADAMTS13[
33], F8[
34] and PDGFRL[
34], which are involved in clotting and have also been observed to be associated with acute Covid-19 severity. Our search reveals limited GWAS studies of long covid[
35,
36] or Covid-19 vaccine adverse events[
37], though GWAS studies of SARS-CoV-2 vaccine antibody responses have been performed[
38,
39] and several mechanistic factors behind the differential vaccine response are identified [
40]. Genetic correlates of vaccine adverse reactions have been studied in the context of Hepatitis B, measles, rubella, and other vaccines [
41].
Several factors impact the immune response to Covid-19 vaccines, including time of day[
42,
43], level of recent sleep [
44,
45,
46,
47] and prior infection[
48]. Several interventions have undergone clinical trials to determine their impact on the vaccine immune response, including iron supplementation (NCT04915820), mushroom mixtures (NCT04951336), immunomodulators (NCT04877496 [
49] and NCT05060991), the ketogenic diet (NCT05163743), metformin (NCT03996538), probiotics (NCT05195151) and osteopathy (NCT04928456 and NCT05069636). Of these trials, only the trial on the immune impact of anti-CD20 therapy has results, which were not significantly different from controls [
49].
The existing study on genetic determinants of Covid-19 vaccine adverse events is very limited[
37]; likewise, we may have to proceed from mechanistic understanding. After endocytosis, the modified mRNA is present in the cytosol to be expressed, which can be highly variable depending on host genetics[
50,
51]. From this point on, the major factor regulating the amount of pathogenic spike protein produced are largely the clearance and degradation mechanisms acting on the chemically modified mRNA. As mentioned before, while pseudouridinylated RNA is far more stable than RNA[
22], the degradation curve of N1-methyl pseudouridinylated RNA is less known, though N1-methyl-pseudouridine in mRNA has been observed to enhance translation[
52]. Individual genetic variation influences the degradation of exogenous RNA [
53].
Furthermore, other wildcards include the potential for reverse transcription into the host genome[
18]. Another point of concern is the observed contamination of mRNA vaccine vials with the DNA plasmid vector[
19], which may possibly be a factor in the observed persistence of spike protein in vaccine injured patients [
3]. This could be explained by transfection of bacteria in the human gut [
54,
55,
56]. Were this a significant factor, we would expect differential vaccine injury susceptibility based on gut microbiota composition. Long covid susceptibility varies according to gut barrier health[
57], and acute SARS-CoV-2 infection severity is negatively associated with gut microbial diversity[
58]. Still, it is unknown to what degree this ‘gut reservoir’ hypothesis for spike protein persistence means. Long covid is associated with higher levels of
Ruminococcus gnavus,
Bacteroides vulgatus and lower levels of
Faecalibacterium prausnitzii [
59].