Phase 1/2 clinical trials of the ChAdOx1 nCoV-19 (AZD1222) vaccine demonstrated an acceptable safety profile and robust immunogenicity. Mild systemic and local reactions, such as fatigue, fever, and headache, were common but peaked on the first day and were mitigated by prophylactic paracetamol. Immunologically, the vaccine induced spike-specific effector T-cell responses that peaked by week two, and serological antibodies that peaked by week four. A second dose further enhanced neutralizing antibody titers, although it did not significantly increase cellular immune responses.

ChAdOx1 nCoV-19 Phase 1/2 Trial Results

ChAdOx1 nCoV-19 (AZD1222) is a chimpanzee adenovirus-vector SARS-CoV-2 vaccine candidate that expresses the full-length spike sequence linked to a tissue plasminogen activator leader sequence. In the supplied phase 1/2 study, adults aged 18–55 received intramuscular ChAdOx1 nCoV-19 or MenACWY, an active control used to help mask vaccine-related reactions. Safety and immune-response findings are covered in the child node.

Tufts University

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SARS-CoV-2 vaccine candidates use several platforms. mRNA and DNA constructs encode viral antigens, adenoviral vectors express the spike protein, and protein-based candidates deliver spike-derived antigen directly. These candidates are evaluated for their ability to elicit adaptive immune responses, including neutralizing antibodies and T-cell responses.

SARS-CoV-2 Vaccine Candidates: Platforms and Immunogenicity

Moderna was one of the earliest companies to propose potential vaccines after having screen through more than 120 mRNA-based molecules. Among them, they identified mRNA-1273 that is capable of triggering the adaptive immune response. This mRNA essentially codes for the viral spike (S) glycoprotein that is involved in receptor recognition with ACE2 receptors in host cells. In the pre-clinical trial experiments with Rhesus macaque, administration of either 10 or 100 micrograms of the mRNA-1273 showed successful induction of type 1 helper T-cells (Th1) and no detectable viral antigens over the course of the next few days. Immunohistochemistry results detected higher levels of IL-21 cytokines. These non-human primates over the course of 2 weeks also showed regression of upper and lower airway infection. 
In the study, there was elevated antibody-binding activity through ELISA detection as well as neutralization activity in vaccinated primates. mRNA-1273 lead to higher suppression of ACE2 binding recognition with spike protein. mRNA-1273 nucleoside modifications and purification were optimized to stimulate the innate immune system in order to enhance translation and duration. One remaining concern was the half-life of antibodies against spike protein. Recent human data shows a reduction of antibodies over time after initial infection. 


Moderna mRNA-1273

BNT162b1 is a lipid nanoparticle–encapsulated, nucleoside-modified mRNA vaccine candidate from Pfizer/BioNTech against SARS-CoV-2, administered by intramuscular injection. Its mRNA encodes the spike glycoprotein's receptor-binding domain (RBD), which is trimerized via an added phage T4 fibritin–derived trimerization domain to raise immunogenicity; incorporating 1-methylpseudouridine increases translation efficiency while still engaging the innate immune response. Because the mRNA does not integrate into the host genome and is only transiently translated to produce the spike antigen that triggers immunity, the platform is considered relatively safe. In the phase 1/2 trials, healthy adults aged 18–55 received the vaccine at 10, 30, or 100 µg or placebo; IgG binding and spike neutralization were dose-dependent. About 7 days after vaccination, both vaccine and placebo recipients reported mild-to-moderate fatigue and headache—more frequently among vaccine recipients—with no fatal events observed. Safety follow-up continues for up to ~6 months and immunogenicity for up to 2 years, and adults over 65 have begun enrolling.

Pfizer BNT162b1

The application of synthetic DNA medicine (INO-4800) in blocking the infection pathway of SARS-CoV-2 have already passed phase 1 of clinical trial on a positive note at Inovio as they now look forward to add participants of older age. Unlike RNA-based vaccine candidates, synthetic DNAs are much easier to design and amplify. They are also more temperature-stable and resistant to nucleases. Previous works done on the MERS-CoV vaccine with INO-4700 as well as Zika virus with GLS-5700 were quite successful in halting infections. These experiences show that INOVIO could potentially apply similar strategies to drive neutralizing antibody responses for long-term protection from COVID-19.
	In general, induction of INO-4800 to African green monkey fibroblast (COS-7) and human kidney (HEK-293T) cell lines both showed substantial levels of antibodies in serum. It is capable of activating cellular and humeral responses within several days post immunization. The receptor binding domain sequence of the spike protein was cloned into pGX9501 and pGX9503 vectors that are transfected into COS-7 and HEK-293T cells showed high levels of RNA levels upon detection by RT-qPCR. Spike protein expression was measured by Western blot to be consistently high and further confirmed qualitatively through immunofluorescence staining. INO-4800 seemed to exhibit competitive inhibition against ACE2 receptor and was also detected in the lungs that halted Lower Respiratory Disease (LRD).


Inovio INO-4800

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Operation Warp Speed

Corum, J., Wee, S., & Zimmer, C. (2020). Coronavirus Vaccine Tracker. https://www.nytimes.com/interactive/2020/science/coronavirus-vaccine-tracker.html

Coronavirus Vaccine Tracker

- Novavex, in collaboration with Takeda, recently developed a protein-based vaccine candidate (NVX-CoV2373) that were constructed from the COVID-19 full-length spike protein, transfected into Spodoptera frugiperda (SF9, fall armyworm) cell lines, and purified. 
- A stable inactivated form of premature S-protein was constructed through mutagenesis by mutating the furin cleavage site as well as incorporating 2 proline substitutions that destabilize the central alpha-helix. 
- Administration of NVX-CoV2373 with Matrix-M adjuvant, a synthetic biomolecule consisting of saponins conjugated to cholesterol and phospholipids, compacted into nanoparticles have shown to induce strong immune responses like Th1 B-cell and T-cell responses as well as secretion of neutralizing antibodies in serum.
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- In preclinical trials, mice were administered in increasing doses of 0.01μg, 0.1μg, 1μg, and 10μg each with 5μg of the Matrix-M. Mice at all dosages exhibit high anti-spike IgG within 3-4 weeks post-initial vaccination. 
- Those vaccinated at 10μg even had complete inhibition of ACE2 receptor binding to spike protein. 
-Even with the smallest dosage, significant amount of inflammatory cytokines like interferon (IFN-γ), tumor necrosis factor (TNF-α), and interleukins (IL-2, IL-4, & IL-5) were secreted from effector memory T-cells. 
- Histopathology of lung tissues showed significant regression of lung tissue inflammation for those administered with NVX-CoV2372 compared to placebo. 
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Description from Lit Review Draft:

"NVX-CoV2373 is a recombinant nanoparticle vaccine composed of trimetric full-length SARS-CoV2 spike glycoproteins and Matrix M1 adjuvant. A randomized, placebo-control, phase 1-2 trial was conducted on 131 healthy adults.  It has high immunogenicity and high levels of neutralizing antibodies. On September 24, 2020, phase 3 clinical trials began and immunized 10,000 people in the next 4-6 weeks. This took place at the Nucleus Network in Herston, Queensland and Melbourne, Victoria.
This vaccine candidate is a recombinant nanoparticle vaccine constructed from full-length wild-type SARS-CoV-2 spike glycoprotein. It includes Matrix M1 Which is a saponin based adjuvant made by Novavax. The rSARS-CoV-2 and Matrix M1 parts were mixed just before use. This vaccine is favorable because it can be stored between 2°C and 8°C, allowing for easy preservation and, therefore, distribution (Novavax Initiates Phase 3 Efficacy Trial of COVID-19 Vaccine in the United Kingdom | Novavax Inc. - IR Site, n.d.)."

Novavax: NVX-CoV2373

Johnson & Johnson and Janssen Pharmaceuticals, in collaboration with Beth Israel Deaconess Medical Center, developed the Ad26.COV2.S COVID-19 vaccine candidate. It utilizes AdVac technology to engineer adenovirus serotype 26 (Ad26) vectors to express the SARS-CoV-2 spike (S) protein, stimulating neutralizing antibody secretion. Following successful application in the Ad26.ZEBOV Ebola vaccine, the Ad26 vector was tested in preclinical trials with rhesus macaques. Subjects were immunized with spike variants and exposed to SARS-CoV-2, identifying Ad26.COV2.S as the most effective candidate for eliciting strong immune responses.

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