mRNA1273 Vaccine
The mRNA1273 vaccine, manufactured by Moderna and the National Institute of Allergy and Infectious (NIAID), is a lipid nanoparticle encapsulated mRNA encodes for SARS-CoV-2 glycoprotein; it has an S1-S2 cleavage site with a transmembrane component [5]. The lipid nanoparticle capsule has four lipids in equal proportions of mRNA and lipid [5].mRNA1273 has an S-2P antigen found on the surface, which allows entry into the cell resulting in an immune response [5].
Preclinical Trials
Preclinical studies conducted on animal models are essential in determining the humoral and cell-mediated immune response following the administration of a vaccine as it helps understand the degree to which a vaccine can provide protection. Since nonhuman primates have substantial similarities to humans in regard to innate immune responses, B cell, and T cell responses, studies conducted on nonhuman primates in preclinical trials allow for appropriate dosage selection and administration in the subsequent human trial populations [6].
During the mRNA1273 preclinical trials, nonhuman subjects were divided into 10 μg and 100 μg dose groups [6]. On week 0 and week 4, six female and six male Indian-origin rhesus macaques, between the ages of 3 to 6 years, were injected intramuscularly with 10 μg or 100 μg in a 1 ml of 1x phosphate-buffered saline (PBS) of the mRNA1273 vaccine [6]. The control group consisted of primates injected with 1x phosphate-buffered saline [6]. On day 56 (week 8), all animals were administered a dose of 7.6 x 105 plaque-forming units (PFU) [6]. 1.9 x 105 PFU/ ml SARS-CoV-2 was injected in a 3 ml solution via the trachea; also, in a 1 ml solution (0.5 ml/ nostril), the respective PFU/ml SARS-CoV-2 was administered via the nasopharyngeal pathway [6]. To assess viral RNA, a polymerase chain reaction was implemented [6]. Duplicating RNA was noted in bronchoalveolar lavage (BAL) fluid, and nasal samples were measured via subgenomic RNA [6]. ELISA measured serum antibodies such as total SARS-CoV-2 S-2P-specific or N-specific IgG [6]. Intracellular cytokine responses were measured using mixture models for single-cell assays (MIMOSA) [6].
Preclinical Trials: Antibody Response & T cell response
Specific antibody responses were noted in the 10 μg and 100 μg dose groups of the mRNA1273 vaccine 4 weeks following the dual dose regimen[6]. IgG binding to the S-2p protein was increased in each dose group: 8241 in the 10 μg dose and 36,186 in the 100 μg dose group. Neutralizing activity was noted via pseudotyped lentivirus reporter 4 weeks following the first vaccination of 10 μg dose group of mRNA1273 vaccine in nonhuman primates consisting of an ID50 geometric mean titer (GMT) of 63. 4 weeks following the second vaccination, GMT levels were detected and subsequently rose to 103 in the 10 μg dose group[6]. The neutralizing activity was also noted 4 weeks following the first vaccination in the 100 μg dose group exhibiting a GMT of 305, which rose to 1862 when the 100 μg dose of mRNA1273 vaccine was administered the second time [6]. These mRNA1273 vaccinated nonhuman primates developed robust serum antibodies specific to the receptor-binding domain; antibodies binding to the specific S1 N terminal domain were observed. A strong and specific immune response was elicited [6]. A live SARS-CoV-2 reporter virus was used to assess the neutralizing activity of the mRNA1273 vaccine indicating a strong S- specific antibody response to the mRNA1273 vaccine [6].
T-cell responses to mRNA1273 were assessed in preclinical trials. 50% (4/8) of the primates in the 10 μg dose group and 100% (7/7) of the primates in the 100 μg dose group developed a dose-dependent Th1 response 4 weeks following the second vaccination [6]. Th1 response was the highest in the 100 μg dose group compared to the control group and the 10 μg dose group [6]. Th2 and CD8+ levels were undetectable in primates injected with mRNA1273 [6].
Phase 1 Clinical Trials
Phase 1 open-label, dose-ranging clinical trials were conducted at the Kaiser Permanente Washington Health Research Institute in Seattle, Emory University School of Medicine in Atlanta, and the National Institutes of Health (Vaccine Research Center Clinical Trials Program) in Maryland, USA. Phase 1 clinical trials were conducted in healthy males and non-pregnant females over 18. Participants received their first vaccination between March 16, 2020, and April 14, 2020 [7][8]. 0.5 mg/ml of the mRNA1273 vaccine was administered in the deltoid muscle of 45 healthy participants. 41% of the participants were female, and 49% were male. 89% of the participants were Caucasian, 13% Hispanic, 4% Black, 2%Asian, and 2% unknown. The age of these participants ranged from 18-55, with a mean age of 33±8.5. On day 1 and day 29 of the clinical trials, participants were given two injections with a 28-day interval between vaccinations. The doses administered in this clinical trial were 25 μg, 100 μg, or 250 μg; each dose group had 15 subjects [8]. Before trials, subjects were not tested for SARS-CoV-2 infection via reverse transcriptase-polymerase chain reaction and serology [8]. Following vaccinations, follow-up visits on days 7 and 14 were standard protocol, including follow-up visits on days 57, 119, 209, and 394 [8]. Of the phase 1 clinical trial population, 3 participants did not receive the second vaccination; 1 participant that was given a 25 μg dose experienced bilateral urticaria of the lower extremities five days following the administration of the first vaccination, and 2 participants failed to follow up due to self-isolation due to suspected COVID-19 [8].
Phase 1 Clinical Trials: Antibody Response & T Cell Response
Pseudovirion neutralization assay (PsVNA), live wild-type SARS-CoV-2 plaque-reduction neutralization testing (PRNT) assay, and ELISA was used to assess the SARS-CoV-2 binding antibodies and neutralizing antibodies[8]. PsVNA and ELISA were assessed on day 1,15,29,36,43, and 57 [8]. PRNT was only assessed on day1 and 43 in the 25μg and 100 μg dose groups[8].
Before the administration of the mRNA1273 vaccine, reaction to pseudovirion neutralization assay (PsVNA) was not observable in any of the subjects participating in the trial; however, reaction to PsVNA was evident in less than 50% of the participants after the first vaccination [8]. However, following the second vaccination, all subjects in this clinical trial had PsVNA responses in their serum [8]. Another neutralization assay used to assess the immune response of the mRNA1273 vaccine was the plaque reduction neutralization test (PRNT). The PRNT assay was assessed in participants before vaccinations showing a lack of 80% live-virus neutralization at 1:8 dilution [8]. However, wild-type virus-neutralizing activity was seen in all participants on day 43. This activity is known to decrease the infectiousness of SARS-CoV-2 by more than 80% (PRNT80) [8].
An intracellular cytokine staining assay was used to gauge the T cell responses produced against the S2P protein. The samples obtained to assess the assay were taken on days 1, 29, and 43 [8]. T cell responses following the administration of mRNA1273 in dosages of 25 μg and 100 μg were noted. The responses elicited by S-specific peptides increased the expression of Th1 cytokines such as tumor necrosis factor-alpha, interleukin 2, and interferon-gamma, whereas Th2 helper cytokine expression of interleukin 4 and interleukin 13 was scarcely seen [8]. Also, low levels of CD8+ T cell responses to the S-2P were observed following the second administration of mRNA1273 at 100 μg dose [8].
Phase 1 Clinical Trials: Adverse Effects
During phase 1 clinical trials, solicited adverse effects such as fatigue, headache, pain at the injection site, and chills were notable in each of the dose groups (25 μg, 100 μg, and 250 μg); as expected, participants in the higher dose groups reported frequent aforementioned adverse reactions following the second dose. Overall, the adverse reactions reported were primarily mild to moderate [9]. No fevers were reported after the first vaccination [9]. After day 7 of each vaccination, more than 50% of the participants reported local and systemic reactions such as local pain at the injection site, myalgias, fatigue, chills, and headaches [9]. Mild adverse effects were noted in the higher dose groups as well as following the second administration of the mRNA1273 vaccine [9]. The Standard Toxicity Grading Scale was used to evaluate the adverse effects [9]. Phase 1 trials were deemed safe, developed antibodies, and induced a neutralizing immune response to the virus [9].
Phase 2 Clinical Trials
From May 29, 2020, to July 8, 2020, randomized, observer-blinded, placebo-controlled, dose-confirmation mRNA1273 vaccine phase 2 clinical trials were conducted to assess the safety, tolerability, immunogenicity, reactogenicity in 600 healthy males and non-pregnant females over the age of 18 in eight clinical research sites across the United States. These clinical trials took place in Kansas, Georgia, Missouri, Nebraska, North Carolina, South Dakota, and Texas [10][11]. All participants were SARS-CoV-2 negative prior to vaccine administration[10][11]. This clinical trial followed the International Council on Harmonization of Good Clinical Practice guidelines. During the screening protocols, exclusion criteria included participants that had a risk of, or were exposed to, SARS-CoV-2 infected individuals or were previously infected with SARS-CoV-2 [11]. The participants in this study were divided into two age cohorts: >18-55 yo age group and >55 yo age group. Each age cohort consisted of 300 randomly divided participants in a 1:1:1 assignment via Interactive Response Technology [11]. The mean age for the 18-55 and >55 age cohorts was 37.4 and 64.3, respectively [11]. The younger cohort comprised 59% females, whereas the older cohort comprised 71% females[11]. The participants in each age cohort were predominantly Caucasians: 92% in the 18-55 age cohort and 97% in the >55 yo age cohort [11]. Participants were administered either a placebo, a 50 μg, or a 100 μg dose of the mRNA1273 vaccine as a dual dose regimen 28 days apart (day 1 and day 29) [11]. Thirteen participants did not complete their vaccination course due to several reasons. One participant experienced SARS-CoV-2-related adverse effects, one participant withdrew consent, two participants experienced adverse effects (1 experienced solicited adverse effects, and 1 experienced a severe adverse effect), five participants failed to follow up, and four others withdrew due to unmentioned reasons[11]. SARS-CoV-2 genomic RNA virus was assessed via nasopharyngeal swabs on days 1, 29, and 57[11]. RT-PCR assay was used to measure the RNA. Before administering the first and second mRNA1273 vaccine, immune responses were assessed on day 1 and day 29, respectively; immune responses were repeatedly detected on days 43, 57, 209, and 394[11]. The generation of serum binding antibodies (bAbs) against SARS-CoV-2 was measured using ELISA[11]. Neutralizing antibodies (nAbs) were measured on day 1, 29, 43, 57, 209, and 394. Seroconversions were measured on days 29, 43, 57, 209, and 394[11].
Phase 2 Clinical Trials: Antibody Response
At baseline, anti-SARS-CoV-2 spike bAbs were not detected in both the control and mRNA1273 vaccine participants [11]. However, 28 days following the first vaccination, anti-SARS-CoV-2 spike bAb were detected in participants that were administered either the 50 μg or the 100 μg dose of the mRNA1273 vaccine. 100% of the participants in phase 2 clinical trials did not have pre-existing neutralizing antibodies at the onset of the study[11]. However, neutralizing antibodies were detected 28 days following the administration of the first dose of the mRNA1273 vaccine[11]. Fourteen days following the second dose of the mRNA1273 vaccine, neutralizing antibodies were detected on day 43 of the clinical study[11]. Compared to the control group, the GMTs generated in both age cohorts with 50 μg and 100 μg doses generated substantial amounts of titers, whereas the control group generated GMTs of 321 with a 95% confidence interval ranging from 235 to 438 μg/ml[11]. In both age cohorts, assessments of the neutralizing antibodies on the subsequent follow-up day 57 (28 days post-dual-dose regimen) did not reveal significant changes in titers compared to day 43 nAbs [11]. Overall, there was a significant rise in neutralizing antibody titers 28 days following the first mRNA1273 vaccine (50 μg and 100 μg doses ) as well as a substantial rise in nAbs 14 days (day 43 of the clinical trials) following the second mRNA1273 vaccine across both age cohorts[11].
Phase 2 Clinical Trials: Adverse Effects
In phase 2 clinical trials, solicited localized and systemic adverse effects were noted. Pain at the injection site was the predominant adverse effect noted in participants. Other adverse effects included headache and fatigue. In both age cohorts, adverse effects were experienced 7 days after the first and second doses of 50 μg and 100 μg of the mRNA1273 vaccine[11]. As expected, vaccine participants experienced greater reactions following their first and second vaccinations as opposed to placebo participants[11].
The most common adverse effect reported via eDiary was pain at the injection site [11]. Other solicited adverse effects that were also reported were myalgia, arthralgia, nausea, vomiting, and chills. The severity of the symptoms increased following the second vaccination among both age cohorts [11]. Grade 3 reactions were increasingly reported following the second vaccination of the 100 μg mRNA1273 for fatigue and myalgia [11]. The mean time period of the solicited adverse effects following the first vaccination ranged from 2.4 -3.1 days in the >18-55 age cohort compared to 2.1- 3.7 days in the >55 yo age cohort. Following the second vaccination, the mean time period of systemic adverse effects ranged from 3-4 days in the 18-55 yo age cohort compared to 1.9-3.4 days in the >55 yo age cohort [11]. Overall, most of the adverse effects experienced by the participants were predominantly mild to moderate. No serious adverse effects and deaths were reported [11].
Table 1 highlights the antibody response from the phase 1 and phase 2 mRNA1273 clinical trials. It also summarizes participant age, dose, and GMT at 95% CI.
Table 1
|
Clinical Trials
|
Phase
|
Age
|
Dose
|
Geometric Mean Titers (GMT) at 95% CI
|
|
Antibody Response
Pseudovirion Neutralization Assay (PsVNA) on Day 43
|
Phase 1
|
|
25 μg
100 μg
250 μg
|
112.3 ( 71.2-177.1) μg/ml
343.8 ( 261.2-452.7) μg/ml
332.3 ( 266.3-414.5) μg/ml
|
|
Antibody Response
Plaque Reduction Neutralization Test (PRNT80) on Day 43
|
Phase 1
|
|
25 μg
100 μg
|
339.7 (184.0-627.1) μg/ml
654.3 (460.1-930.5) μg/ml
|
|
Antibody Response Detection of Neutralizing Antibodies (nAbs) on Day 43
|
Phase 2
|
18-55
>55
|
50 μg
100 μg
50 μg
100 μg
|
1733 (1611 -1865) μg/ml
1909 (1849 -1971) μg/ml
1827 (1722 -1938) μg/ml
1686 (1521 -1869) μg/ml
|
|
Antibody Response Detection of Anti-SARS-CoV-2 Spike Binding Antibodies (bAbs) on Day 43 and Day 57
|
Phase 2
|
18-55
>55
|
50 μg
100 μg
50 μg
100 μg
|
189 (173 - 207) μg/ml | 146 (132 -161) μg/ml
239 (221 - 259) μg/ml | 181(164 -200) μg/ml
153 (135 - 175) μg/ml | 107 (93 - 123) μg/ml
162 (142 - 185) μg/ml |121 (105 -139) μg/ml
|
Table 1: This table represents the antibody response from the phase 1 and phase 2 mRNA1273 clinical trials, including participant age, dose, and GMT at 95% CI.
Phase 3 Clinical Trials
On July 27, 2020, a phase 3 randomized, placebo-controlled, observer-blinded clinical trial for the mRNA1273 vaccine was commenced across 99 centers in the United States, enrolling 30, 420 healthy, ethnically diverse volunteers over the age of 18 of which 79.2% were Caucasian, 20.5% Hispanic, and 10.2% African American. The average age of the participants in the clinical trials was 51.4 years old. 47.3% of the participants were female. 24.8% of the total number of participants were >65 years of age, and 16.7% were under the age of 65 with pre-existing medical conditions [12][13]. Participants were equally divided into two groups via random assignment of 1:1 ratio: 15, 210 participants in the placebo group and 15, 210 participants in the mRNA vaccine group. At baseline, only 2.3% of the participants from the mRNA vaccine group had been infected with SARS-CoV-2 [13]. During the duration of the clinical trials, only 11 participants tested positive for COVID-19 in the mRNA1273 vaccine group[13]. Additionally, over 96% of the participants completed the dual-dose regimen 28 days apart (placebo and mRNA1273 vaccine)[13]. The remaining 4% of the total number of participants did not receive the second dose due to consent withdrawal or positive SARS-CoV-2 via polymerase chain reaction test on day 29. 153 of these participants withdrew consent, and 114 participants (69 participants in the placebo group, 45 participants in the mRNA1273 vaccine group) were SARS-CoV-2 positive prior to the scheduled second dose; therefore, they did not receive the second dose[13].
Phase 3 Clinical Trials: Adverse Effects
Common adverse effects were assessed 7 days following the administration of the first and second dose of the placebo and mRNA1273 vaccine[13]. The most commonly reported adverse effect included grade 1 or 2 pain at the injection site; this pain subsided within 2.6 days following the first dose and 3.6 days following the administration of the second dose[13]. Participants in the mRNA vaccine group reported a greater number of solicited adverse effects compared to the placebo group[13]. After the first dose, 84.2% of the mRNA1273 vaccine group reported symptoms[13]. Following the administration of the second vaccination, 88.6% of the participants in the mRNA1273 vaccine group reported common adverse effects[13].
Additionally, 244/30,420 participants experienced delayed onset of local adverse effects on day 8 post-vaccination of the first dose[13]. Eight days following the second dose, 68/30,420 participants experienced delayed onset of adverse reactions. Solicited localized adverse reactions such as erythema and tenderness subsided within 4-5 days of onset[13].
In terms of solicited systemic adverse effects, following the administration of each of the scheduled first and second doses, the mRNA1273 vaccine group experienced systemic symptoms frequently compared to the placebo group [13]. After the first dose, 54.9% of the participants in the mRNA1273 vaccine group reported systemic symptoms compared to 79.4%following the second dose[13]. Notably, systemic symptoms were greater following the second dose of the mRNA1273 vaccine group; symptoms markedly increased to grade 2 and 3 levels[13].
Grade 2 systemic events increased from 16.5% following the first dose to 38.1% following the second dose[13]. In addition, grade 3 systemic events increased from 2.9% following the first dose to 15.8% following the second dose[13]. The duration of the systemic adverse reactions after the first and second dose subsided within 2.9-3.1 days[13]. Participants between the ages of 18-65 frequently reported both localized adverse reactions and solicited systemic adverse reactions post-vaccination compared to participants over the age of 65[13].
Overall, localized adverse reactions were mild[13]. Additional localized adverse effects that were reported were myalgia, fatigue, and arthralgia following the second dose of the mRNA1273 vaccine[13]. Importantly, individuals that tested positive for SARS-CoV-2 during enrollment in phase 3 clinical trials experienced fewer solicited adverse effects compared to the large number of participants that tested negative for SARS-CoV-2 at baseline[13].
Two deaths were reported in the mRNA1273 vaccine group due to cardiopulmonary arrest and suicide, respectively[13]. Hypersensitivity reactions were noted in a small percentage of participants in both placebo and mRNA1273 vaccine groups[13]. Bell's Palsy was noted in 1 participant from the placebo group and 3 participants in the mRNA1273 vaccine group[13]. Additionally, exacerbation of respiratory distress or other respiratory-related medical conditions was not observed following the dual dose regimen of the mRNA1273 vaccine[13].
Phase 3 Clinical Trials: Delayed Large Localized Adverse Effects
During phase 3 clinical trials, delayed adverse effects were noted following the administration of the dual dose of the mRNA1273 vaccine. Dose 1 post-vaccination exhibited delayed adverse effects between day 4 and day 11, with a median onset on day 8[14].
A case series of 12 mRNA1273 vaccine recipients were observed; the initial solicited adverse effects (local and systemic symptoms) completely resolved before the second bout of adverse effects[14]. These delayed localized effects were observed near the injection site with diverse presentations[14]. 5/12 vaccine recipients presented with plaques that were ≥10 cm in diameter (Grade 3 plaque)[14]. Some 5/12 recipients experienced simultaneous systemic adverse effects and cutaneous manifestations[14]. Most patients exhibiting these delayed adverse effects were treated accordingly with ice and antihistamines, while some were treated with topical, oral, or both glucocorticoids for symptomatic relief. However, one vaccine recipient received an antibiotic for suspected cellulitis[14].
The suspicion of delayed-type or T-cell-mediated hypersensitivity reactions following the administration of the first dose of mRNA1273 was confirmed via a skin biopsy conducted on a patient not part of the case series study[14]. The skin biopsy revealed superficial perivascular and perifollicular lymphocytic infiltration with scarce eosinophils and dispersed mast cells[14].
Following the second dose administration, 6/12 vaccine recipients experienced recurrent adverse reactions. 3/6 experienced similar symptoms, and clinical presentation as the first dose delayed adverse reactions; the remaining 3/6 vaccine recipients reported delayed localized reactions post-vaccination as lower grade than the first dose[14]. Cutaneous manifestations occurred earlier than the first dose, ranging from day 1 to day 3, with a median onset of day 2 [14].
Phase 3 Clinical Trials: Efficacy
During the phase 3 clinical trials, the efficacy of the mRNA1273 vaccine was assessed during the primary, secondary, and per-protocol analysis[13]. The primary analysis included assessing the number of participants infected with SARS-CoV-2 in the placebo group and vaccine group[13]. A total of 196 participants tested positive for SARS-CoV-2, of which only 11/ 196 SARS-CoV-2 positive participants were in the mRNA1273 vaccine group[13]. This reflected a 94.1% efficacy with a 95% confidence interval ranging from 89.3 to 96.8% with a P <0.001. This reflects the mRNA1273 vaccine's ability to prevent SARS-CoV-2 infection[13]. In the secondary analysis, participants were assessed 14 days after administering the first dose. Only 11/236 participants tested positive for SARS-CoV-2 in the mRNA1273 vaccine group reflecting a 95.2% efficacy with a 95% confidence interval ranging from 91.2 to 97.4% [13]. In the per-protocol analysis, participants who tested positive for SARS-CoV-2 during the onset of the clinical trials were also assessed; 199 participants were SARS-CoV-2 positive at baseline; among the 199 participants, 187 cases were in the placebo group, whereas 12 cases were in the mRNA1273 vaccine group[13]. Between day 1 and day 42, 7 participants tested positive for SARS-CoV-2 in the mRNA1273 group, while 12 participants from the placebo group tested positive for SARS-CoV-2 within the same time frame; this reflected a vaccine efficacy of 93.6% with a 95% confidence interval ranging from 88.6 to 96.5 [13]. It is important to note that during the clinical trials, 30 participants in the placebo group had severe COVID-19 infection; 1 participant from this group succumbed to the disease [13]. Overall, vaccine efficacy was noted to fare well among all subgroups such as age, sex, and race-ethnicity in elderly and young age groups.
Phase 3 Clinical Trials: Approval
On December 18, 2020, mRNA-1273 SARS-CoV-2 was granted emergency use authorization by the FDA, making it the second mRNA vaccination presented by a EUA following the Tozinameran (BNT162b2) vaccine. On January 31, 2022, precisely 13 months and one week later, the Elasomeran (mRNA1273) vaccine was granted full FDA approval for use in people 18 years of age and above for COVID-19 prevention. This is also the second vaccine to receive full FDA approval, following the Tozinameran (BNT162b2) vaccine, which received FDA approval on August 23, 2021. The mRNA vaccine is now distributed as "Spikevax". It may be given interchangeably as a two-dose series (0.5 mL each) administered four weeks apart from the initial Moderna COVID-19 Vaccine that was originally issued EUA. As part of the primary two-series dosage, a third dose can be given to immunocompromised individuals 18 years of age and above. A booster vaccination may also be given five months following the completion of the initial two doses in individuals 18 years of age and above.