1. Introduction
Pharmaceutical and medical device approvals are based in structured approval processes and historically, the track record for approval has been far from ideal. There are many examples of over-turnings of approvals of pharmaceuticals post facto, due to emergence of oversights of particular safety factors that had occurred during the approval process [
1]. The former examples represent failures in regulatory bodies to sufficiently assess safety during this process and this can be quite costly both in terms of potential economic and individual harms [
2]. To put this ever-present issue into perspective, of 309 novel cardiovascular, orthopaedic and neurologic devices approved in the EU between 2005 and 2010, 73 (24%) were subject to either a safety alert or product recall [
3], consistent with other reported rates [
4]. Importantly, as complexities and novelties of products are increasing, approval success rates have been decreasing [
5] and in the face of new drug approvals currently marred by low Phase III trial success rates (~10%), this is an issue in dire need of acknowledgement and remedy [
6]. The precautionary principle dictates that caution must be exercised in the context of potential safety issues with novel drugs and technologies, and thus due to the low success rates of novel and unprecedented drugs [
6,
7,
8], and the potential risks to the population, it is important to adopt the
precautionary principle [
9] when approving any pharmacological products, especially those given to large populations. COVID-19 mRNA products are novel with regard to their delivery system and their content as the first mRNA vaccines approved for use in humans, as well as the first approved coronavirus vaccine in humans. The speed at which they were designed, developed, approved and administered is also unprecedented in pharmaceutical history [
10] and defies traditional timelines for testing of biological products for use in humans.
Given the approval of the mRNA platform by health regulators across the globe, industry is poised to develop new vaccines using mRNA, as it is a versatile platform which only requires the genetic sequence of the target antigen. The administration of billions of doses has resulted in great industry enthusiasm for the platform, and other mRNA products are being developed using the same core technology [
11,
12].
To assess the novelty of COVID-19 mRNA products, we look back to the history of mRNA vaccines, which begins with experiments on in-vitro transcribed RNA, i.e., delivering RNA to a cell for expression of a protein of interest. Synthetic RNA technology has a wide variety of applications, from the delivery of small interfering RNAs (siRNAs) to reduce gene expression, or messenger RNAs (mRNAs) to encode for a protein of therapeutic value, or to encode for an antigen to stimulate an immune response, as in the strategy of mRNA vaccination.
Early attempts to express proteins from injected mRNA faced several challenges. First, bare RNA produces an inflammatory response, limiting the expression potential of the RNA, as it is broken down. Secondly, it is difficult for the bare RNA to enter through a cell membrane. These issues were addressed through the processes of pseudouridinylation and encapsulation in a lipid nanoparticle (LNP) respectively. The former discovery decreased the lability of RNA, enabling it to remain in the body for longer periods of time. The latter discovery not only shielded the RNA from the host’s immune response as well as RNAses, it also enabled efficient uptake by cells, where it could be efficiently translated by host ribosomes. Pseudouridine was later replaced by m1-methyl-psuedouridine, owing to its greater translation fidelity, higher expression, and better evasion of the host immune response.
LNP development was improved through two innovations, PEGylation, and the use of cationic lipids. LNP surface modifications by poly-ethylene glycol (PEG) enabled lipid nanoparticles to survive for longer lengths of time still, so that their package contents could be delivered to cells to provoke an immune response when the antigen is expressed. Another important development for LNPs is the use of cationic lipids; enabling efficient self-assembly and encapsulation of the mRNA. Cationic lipids can additionally be modified to deliver drugs to certain cell types, an important consideration when delivering mRNA.
There is a prior history of drug delivery by lipid nanoparticles (LNP), and one approved drug for the delivery of a small interfering RNA (Onpattro [
13]). Questions remain pertaining to the safety of mRNA vaccines, as several assumptions on which they were rapidly approved, have been either challenged or overturned by experimental [
14] and clinical evidence [
15]. Quoted theoretical safety advantages were the ease of production without contamination (mRNA vaccines do not require live virus production), and lower (in theory non-existent) risks of infection or host genome integration [
16]. Beforehand, concerns existed over the induction of Type I interferon responses by mRNA vaccines [
17,
18], which are associated with inflammation and autoimmunity [
19,
20].
For example, the dual assumptions that LNPs remain at the injection site, and that the mRNA degrades quickly have been shown to be false; biodistribution and bioaccumulation data indicate that LNPs can enter the bloodstream [
14,
21,
22,
23,
24,
25], and peer-reviewed studies have shown durability of both mRNA and spike protein for
in vivo [
23] and up to 4 months post injection for spike protein [
21]. Given the novelty of mRNA vaccines, and the increasing evidence of harm from clinical reports [
15], epidemiology [
26] as well as laboratory science [
27], there are open safety concerns to be addressed by future research.
Multiorgan vasculitis, with notable involvement of small vessels, is now emerging as a common theme underlying adverse events following COVID-19 vaccination. Affliction of capillaries with thrombus formation in brain and heart are repeatedly being observed [
28,
29,
30]. This pattern of disease in small and smallest vessels is novel and deemed by the authors to be characteristic for the action of mRNA-based vaccines.
The outcome with future mRNA vaccines against other pathogens will be much the same as we have witnessed with the COVID-19 vaccines. It is true that the spike protein itself can promote blood clotting and inflammation without any help from the immune system [
31]. Nevertheless, the available evidence indicates that the grave, widespread and sustained injury to tissues and to blood vessels is mostly caused by the immune attack on spike protein-producing cells. This attack occurs simply because the spike protein is a non-self antigen; and since every other mRNA vaccine will encode its own non-self antigen, derived from whichever particular microbe it targets, we must expect that it will cause harm by the same mechanism and to a similar extent. These scenarios will worsen with each successive booster.
This review summarizes known mechanisms of harm specific to mRNA vaccines, where we examine historical data on mRNA vaccines to determine if safety signals were apparent during production or testing. Prior to the trials on COVID-19 vaccines involving tens of thousands of people, public data existed on only 285 people administered mRNA vaccines, with the earliest trials finishing in 2018 and exhibiting high rates (>10%) of severe adverse events (
Supplementary Table S1). The novelty of mRNA/LNP products must be stressed in guiding their safety assessment, as current approvals still leave many questions unanswered, and serious risks cannot be definitively ruled out based on current evidence.
Figure 1.
Overview of mRNA-LNP vaccine components.
Figure 1.
Overview of mRNA-LNP vaccine components.
In this review, we summarize what is known about the individual components of mRNA vaccines individually, by reviewing literature on past therapeutics. Additionally, we review the known safety impacts of mRNA vaccines prior to COVID-19, as well as other coronavirus vaccines which, while using a non-mRNA platform, inform us of safety risks when vaccinating against coronaviruses.
3. Discussion
There is limited information to make a safety assessment of mRNA vaccines. In the category of mRNA vaccines, there are patient data for 385 patients. For mRNA vaccines against an infection, there was patient data for 285 patients. The rate of serious adverse events was 64 out of 385 for the broad category of RNA vaccines (including cancer vaccines), or 17%; restricting the definition to vaccines against infection, the rate of SAEs is 41/285 or 14%. While high levels can be expected for trials of a novel technology where dosage levels must be determined (many of these trials are phase I) [
163], these findings showcase the relative immaturity of mRNA vaccination as a strategy. Given the low efficacy and short duration of protection of SARS-CoV-2 mRNA products [
164,
165], and the low risk of many populations from COVID-19 complications [
166], it may be advisable for the suspension of mRNA vaccines in certain risk cohorts.
The key to the reactivity of mRNA vaccines is the fact that they express a foreign antigen, for which the antigen presenting cells are marked for destruction. While the lipid nanoparticle exhibits an acute inflammatory response by itself [
39,
40,
167], the trials using LNPs so far have not found a large safety signal when using LNPs to deliver small molecules, non-expressing RNAs, or RNAs for endogenous proteins [
39,
40,
167].
In addition to there being harms attributable to the general immune response from an LNP-RNA delivery system, there are also some harms specific to the spike protein. Several of these mechanisms are supported by laboratory experiments and clinical findings but need more investigation. Medicine is replete with cases for which safety was assumed without adequate evidence at the time, which later regretfully led to loss of health and life. mRNA vaccines are demonstrating great unintended harms, and these harms demand further investigation into mechanism, which is important for identifying treatment modalities.
Novel biomedical technologies can bring relief to a wide variety of conditions and diseases. However, their use must take into consideration their possible harms. Here, we argue that the mRNA technology is novel enough that safety concerns in current and future products cannot be definitively ruled out, and further research must be performed to ensure their safety for current and future users. Considering the lack of data on the platform itself, we recommend a robust, independent and wide-ranging safety audit of mRNA-LNP formulations and call on regulators to hold manufacturers to high safety standards, especially for products used prophylactically in the general population.