Death after the Administration of COVID-19 Vaccines Approved by EMA: Has a Causal Relationship Been Demonstrated?

More than eight billion doses of COVID-19 vaccines have been administered globally so far and 44.29% of people are fully vaccinated. Pre-authorization clinical trials were carried out and the safety of vaccines is still continuously monitored through post-commercialization surveillance. However, some people are afraid of vaccine side effects, claiming they could lead to death, and hesitate to get vaccinated. Herein, a literature review of COVID-19-vaccine-related deaths has been carried out according to the PRISMA standards to understand if there is a causal relationship between vaccination and death and to highlight the real extent of such events. There have been 55 cases of death after COVID-19 vaccination reported and a causal relationship has been excluded in 17 cases. In the remaining cases, the causal link between the vaccine and the death was not specified (8) or considered possible (15), probable (1), or very probable/demonstrated (14). The causes of deaths among these cases were: vaccine-induced immune thrombotic thrombocytopenia (VITT) (32), myocarditis (3), ADEM (1), myocardial infarction (1), and rhabdomyolysis (1). In such cases, the demonstration of a causal relationship is not obvious, and more studies, especially with post-mortem investigations, are needed to deepen understanding of the possible pathophysiological mechanisms of fatal vaccine side effects. In any event, given the scarcity of fatal cases, the benefits of vaccination outweigh the risks and the scientific community needs to be cohesive in asserting that vaccination is fundamental to containing the spread of SARS-CoV-2.


Introduction
Since severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread worldwide, the international scientific community has been focused on developing strategies to contain it [1,2]. Thanks to its efforts, to date, SARS-CoV-2 infection can be counteracted not only with simple preventative measures (e.g., face masks, handwashing, and physical distancing) but also with effective vaccines [3,4]. According to the Centers for Disease Control and Prevention (CDC), a vaccine is "a preparation that is used to stimulate the body's immune response against diseases" [5]. More than eight billion doses of COVID-19 vaccines have been administered globally so far, and 44.29% of people are fully vaccinated [6,7]. Regarding the European Union, about 660 million doses have been administered and more than 290 million (298,845,193) people are fully vaccinated [8]. COVID-19 vaccines, due to the urgency of the global pandemic, were given emergency approval [9][10][11][12]. Clinical trials counting thousands of participants were carried out before the authorization [13,14]. Moreover, since the vaccines' administration to the population was authorized, (ADEM) in one case (1.8%); massive cerebral hemorrhage not associated with thrombosis or auto-antibodies in one case (1.8%); anaphylactic reaction to anesthetics associated with cerebral venous sinus thrombosis and anti-PF4 antibodies in one case (1.8%); hyperglycemic coma in one case (1.8%); hemorrhagic shock due to aortic dissection with rupture in one case (1.8%); complications of rhabdomyolysis in one case (1.8%). Figure 2 shows the distribution of the causes of death among the cases.  Table 1. A summary of the main information obtained from the results of our literature review. AAT indicates acute aortic thrombosis; ADEM, acute disseminated encephalomyelitis; AF, atrial fibrillation; CBN, contraction band necrosis; CeVD, cerebrovascular disease; CI, cardiac insufficiency; CND, chronic neurologic disorder; COPD, chronic pulmonary disease; COVID-19, coronavirus disease 2019; CRP, C-reactive protein; CRF, chronic renal failure; CSF, cerebrospinal fluid; CVST, cerebral venous sinus thrombosis; DIC, disseminated intravascular coagulation; DM2, type 2 diabetes mellitus; DVT, deep vein thrombosis; FXIII, coagulation factor XIII; FVL, Factor V Leiden; HL, hyperlipidemia; HT, hypertension; IHD, ischemic heart disease; IL, interleukin; LN, lymph node; MI, myocardial infarction; MTHFR, methylenetetrahydrofolate reductase; NP, not performed; NS, not specified; PAD, peripheral artery disease; PAE, pulmonary embolism; PC, pseudomembranous colitis; PF4, platelet factor 4; PSC, primary sclerosing cholangitis; RA, rheumatoid arthritis; SplVT, splanchnic vein thrombosis; SVT, superficial vein thrombosis; VITT, vaccine-induced immune thrombotic thrombocytopenia. ↓ indicates reduction of levels.  The distribution concerning the type of vaccine was as follows: 35 cases of death following the Vaxzevria ® (63.6%), 9 cases following the Comirnaty ® (16.4%), 6 cases following the Spikevax ® (10.9%), and 5 cases following the Janssen ® (9.1%). Figure 3 illustrates the distribution of the type of vaccine among the 55 cases.  Figure 4 shows the distribution of the probability of the causal relationship among the 55 cases. In Table 2, the distribution of causes of death per type of vaccine is shown. The cases in which the causal relationship between the vaccine and the death was not demonstrated or was improbable have not been included in this table.
Comirnaty ® and Spikevax ® work by introducing a piece of mRNA that contains the instructions for synthesizing the Spike protein, a surface protein that acts as a key allowing the virus to enter the cells. Once the human cells produce the Spike protein, they rapidly break down the mRNA [37][38][39]. This is the first time an mRNA vaccine has been administered to the population.
Ad26.COV2.S and ChAdOx1 are viral vector vaccines. They use an adenovirus to deliver a DNA genetic sequence encoding for the Spike protein into the cells [40]. Adenoviruses have already been used as vaccine agents in other infectious diseases, such as the Ebola infection [41].
It is necessary to overcome COVID-19 vaccine hesitancy to achieve a high percentage of vaccinated people [42]. However, some people are procrastinating and rejecting the vaccine because of the fear of death due to its side effects. They claim that these vaccines are new and therefore have not been studied enough to be safe [43][44][45][46][47][48][49]. Indeed, COVID-19 vaccines may cause side effects, as any other drug. The most common are mild and short-lived, such as fever, administration-site pain, weakness, etc. [50,51]. In addition, some severe adverse reactions have occurred. Regarding the mRNA vaccines, myocarditis, pericarditis, and anaphylaxis have been described, but these cases are very rare [52,53]. Moreover, it has been demonstrated that the viral vector vaccines can cause venous thrombosis associated with thrombocytopenia, so-called vaccine-induced immune thrombotic thrombocytopenia (VITT), and very few cases of Guillain-Barré syndrome have been reported [54][55][56].
We found 55 cases of death temporally related to COVID-19 vaccine administration. The male/female ratio was close to one (1.04), showing no difference between sexes. The ratio between people aged 50 years or younger and older than 50 years was 0.8. So, it seems there is a slight predominance of older people among the cases. This is quite interesting, as we would have expected a more pronounced difference. Some possible reasons are that the death of a young person arouses greater interest, inducing the performance of investigations, and is more likely to be reported.
As mentioned before, more than eight billion doses of COVID-19 vaccines have been administered worldwide. However, searching the literature, we found only 55 cases of death temporally correlated with vaccination, and in 17 of these a causal relationship has been excluded. Therefore, these 17 cases of death are only temporally, and not causally, related to the vaccine administrations. Among the remaining 38 cases, in eight the probability of a causal correlation between the vaccine and the death was not specified, in 16 the authors stated that it was possible or probable, while in 14 cases the causal relationship was very probable/confirmed. The causes of death which can be considered vaccine-related were the following: VITT (27 cases with ChAdOx1, 4 cases with Ad26.COV2.S, and 1 case with mRNA1273), myocarditis (two cases with BNT162b2, one case with mRNA1273), acute disseminated encephalomyelitis (ADEM, one case with ChAdOx1), myocardial infarction (one case with Ad26.COV2.S), and complications of rhabdomyolysis (one case with mRNA1273). The ratio of deaths to the total number of administered vaccine doses (55 vs. millions of doses) clearly shows how rare fatal adverse events are, as has been found for other vaccines (for example, quadrivalent live attenuated and trivalent inactivated influenza vaccines) [57][58][59]. Moreover, the effectiveness of the vaccination programs in preventing hospital admission and COVID-19-related deaths has already been demonstrated [60,61]. Vaccines are the principal preventive strategy. Moreover, recent studies have shown the efficacy of new therapies in controlling the disease: monoclonal antibodies and antiviral drugs (e.g., molnupiravir, nirmatrelvir/ritonavir) [62]. In the future, the development of more effective vaccines (e.g., sterilizing immunity), the high percentage of vaccinated people-also in the developing countries-and effective therapeutic protocol will make COVID-19 a disease to live with [63].
A brief discussion about the assessment of the link between the vaccines and the deaths (causal or only temporal) is provided below.

Vaccine-Induced Immune Thrombotic Thrombocytopenia
VITT is characterized by moderate to severe thrombocytopenia associated with venous and/or arterial thrombosis mainly in unusual locations, such as the cerebral venous sinus or the splanchnic veins [64]. The serum of the patients affected by VITT contains autoantibodies against the platelet factor 4 (PF4) antigen that can be identified by PF4 enzyme-linked immunosorbent assay (ELISA) [65]. VITT features resemble those of autoimmune heparin-induced thrombocytopenia (HIT) [25,33,66]. The production of PFA autoantibodies induces platelet activation through the formation of PF4-polyanion complexes, causing thrombocytopenia, disseminated intravascular coagulation, and atypically located thrombotic events. Even if the reason why the vaccine triggers the production of autoantibodies has not been disclosed yet, the causal relationship between VITT and adenoviral vector COVID-19 vaccines is confirmed [67]. Interestingly, we found a case of VITT related to an mRNA vaccine [31]. Even if this case is anecdotal, it suggests that VITT is not only related to adenoviral vectors and that other factors are implicated in its pathophysiology.
To confirm VITT in suspected cases, several recommendations have been published and diagnosis is based on anti-PF4 antibodies testing [68,69]. Therefore, the causal relationship between the death and the vaccine in such cases is quite easy to demonstrate or exclude.

Myocarditis
Myocarditis is a myocardium inflammation with myofiber damage and necrosis [70,71]. It is caused by various events, e.g., viral infections, drugs, etc., and it can lead to severe symptoms and death, even in young people [72,73]. Myocarditis has been reported as a side effect of vaccinations, such as influenza, hepatitis B, etc. [74]. So, it is not surprising that COVID-19 vaccines could also cause myocarditis. We found three cases of death from mRNA vaccine-related myocarditis. Cases of non-fatal myocarditis and pericarditis have also been reported [75][76][77][78][79][80][81]. Indeed, EMA warned about the risk of myocarditis and pericarditis with COVID-19 mRNA vaccines [52]. Moreover, the CDC Advisory Committee on Immunization Practices recognized that COVID-19 mRNA vaccines can cause myocarditis [82]. However, such events are rare, and even COVID-19 itself can cause myocarditis and pericarditis [83][84][85][86]. Therefore, the vaccine's benefits overcome the risks [87]. When a case of myocarditis or pericarditis occurs after a vaccination and without an alternative cause, a causal link with the vaccine is generally considered to be present or at least possible, even if a specific diagnostic test or laboratory analysis is not available [88,89]. Ante-mortem and post-mortem investigations can demonstrate features of myocarditis (for example, histologically) but cannot differentiate its etiology.

Acute Disseminated Encephalomyelitis
ADEM is an inflammation of the central nervous system associated with demyelination [90,91]. The clinical trials performed to evaluate the safety of the COVID-19 vaccines before general administration did not highlight cases of ADEM [92,93]. However, the AstraZeneca initial trial was provisionally stopped due to two cases of transverse myelitis that eventually were not considered to be undoubtedly related to the vaccine [94]. In the case of death due to ADEM after Vaxzeria administration reported in this review, the pathological mechanism that induced the encephalomyelitis was not clear and the authors did not state with certainty that it was causally related to the vaccine [28]. Another case of neuroinflammatory disorder after a COVID-19 mRNA vaccine (Comirnaty) has been published and some cases of ADEM have been reported in some international and national side effects reporting systems, such as the Vaccine Adverse Event Reporting System (VAERS) and EudraVigilance [95,96]. In such situations, given the fact that only anecdotal cases are reported in the literature, it is not possible to demonstrate a causal link with the vaccine, even in the absence of alternative causes. The risk of ADEM or other severe neurological disorders seems to be extremely low with COVID-19 vaccines. Vice versa, COVID-19 patients can manifest neuropathological features due to the infection, so the balance between risks and benefits is in favour of the vaccine [97].

Rhabdomyolysis
Rhabdomyolysis is due to the damage of the muscle that induces the release of intracellular myoglobin into the blood [98]. The consequent accumulation of myoglobin in the kidneys causes tubular necrosis and acute renal failure [99,100]. In the case of death after a COVID-19 vaccine (mRNA1273) described by Ajmera, the patient was hospitalized because of rhabdomyolysis, developed pneumonia and other complications, and then died [18]. Post-mortem investigations were not performed. Other cases of rhabdomyolysis after COVID-19 vaccination have been reported, both in the literature and in the side effects reporting systems (e.g., VAERS) [101][102][103][104][105][106][107][108][109]. Again, it is difficult to assess whether the link between the rhabdomyolysis is causal or only temporal and the diagnosis of vaccine-induced rhabdomyolysis is based on the exclusion of other causes.

Myocardial Infarction
The commonest cause of acute myocardial infarction is coronary artery occlusion due to the rupture and/or erosion of a vulnerable plaque, with consequent thrombus formation [110][111][112][113][114][115][116]. During the COVID-19 outbreak, there has been a reduction of cases of patients presenting with myocardial infarction [117,118]. However, even some cases of myocardial infarction induced by SARS-CoV-2 infection have been described [119]. The underlying pathological mechanism may involve acute plaque alterations induced by inflammation and cytokines [120][121][122]. Concerning COVID-19 vaccines, we found only one case of death due to acute myocardial infarction possibly related to Janssen vaccine administration [32]. Actually, the case is about a 69-year-old man who developed CVS thrombosis with anti-PF4 autoantibodies alongside coronary thrombosis. Myocardial histology showed fresh myocardial ischemia, while the cerebral tissue did not show any significant alteration. The authors attributed the death to acute myocardial infarction. The man died at home, so clinical information is not available. This is a peculiar case because the patient could also have been diagnosed with VITT, even if it was not the cause of death. The coronary thrombosis may also be related to the pro-coagulation state induced by the antiPF4 autoantibodies. Indeed, antiPF4/heparin antibodies seem to be an independent predictor of myocardial infarction in patients with acute coronary syndrome, suggesting that it may be involved somehow in the pathophysiology of such disease [123].
In any event, we must be clear that in our review we found other cases of myocardial infarction, both acute and recurrent, after COVID-19 vaccines, but in such cases the authors did not state there was a causal link. The relationship was considered to be only temporal. Edler et al. described the case of an old man with several comorbidities who was found dead at home two days after receiving a first dose of Comirnaty ® (see Table 1) [23]. The autopsy revealed features of peripheral pulmonary embolism and recurrent myocardial infarction. Schneider and colleagues reported three cases [32]. The first is that of an obese 34-year-old woman who was found dead at home the day after receiving a first dose of Vaxzevria ® . Fresh myocardial ischemia along with myocardial scars and hypertrophy were the main autoptic findings. The second case regards a 57-year-old man who died two days after Vaxzeria ® administration (unknown dose). Again, the autopsy revealed cardiac hypertrophy, myocardial scars, coronary sclerosis, and a fresh myocardial infarction. The third case is that of a 72-year-old woman who died in the vaccination center soon after Comirnaty ® administration. The first hypothesis was an anaphylactic reaction, but the autopsy showed coronary sclerosis, myocardial scars, coronary thrombosis, and acute myocardial infarction, while the anaphylaxis diagnostics were negative. In these cases, it was not possible to establish a causal relationship between the vaccine and acute myocardial ischemia, so the causal relationship was not determined.
The relatively high frequency of death and sudden death due to myocardial infarction and the high number of administered COVID-19 vaccine doses each day may suggest that there is only a casual and chronological relationship between the two events. In any case, we think further studies are needed to deepen this topic. We suggest in such cases to perform the VITT diagnostics and to look for anti-PF4 autoantibodies, as in the case previously described, to verify if they could be involved in myocardial infarction after the COVID-19 vaccination.
A limit of our study is the small sample size and the fact that the cases collected in this review do not represent the whole number of deaths after COVID-19 vaccine. We think there could be a sort of "reporting bias" concerning this type of event. At first, researchers could be inhibited from reporting cases of vaccine-related death because of the fear of being held up as "no-vax". In addition, we noticed that authors tended to be prudent in stating whether or not there was a causal correlation between a vaccine and a death. In fact, in eight cases the causal relationship was not explicitly established. Therefore, post-mortem investigations should be considered essential since the autoptic data and histological analysis could provide more information about the pathological features in such cases of death.

Conclusions
Given the current pandemic situation, it is fundamental that most people get vaccinated. Concerns about vaccines' side effects and consequent hesitancy are serious factors that slow down the immunization campaign; thus, the scientific community needs to be cohesive in maintaining that vaccination is fundamental to containing the spread of SARS-CoV-2 [124][125][126][127]. However, it is just as important to evaluate the safety of these vaccines and continuously monitor potential side effects. In this study, we examined 55 cases of death following COVID-19 vaccination reported in the literature to analyze all the available data on fatal cases and assess the existence of a possible correlation with vaccine administration. Given the small number of severe adverse reactions and deaths reported, it is beyond doubt that the benefits of vaccination outweigh the risks. Nevertheless, we think more studies are needed to deepen understanding of possible vaccine-related pathophysiological mechanisms, and researchers should report such cases. Furthermore, we want to encourage post-mortem investigations in cases of death following COVID-19 vaccination because they are essential to better clarify whether a causal relationship between vaccination and death does exist.