Table 1 COVID-19 vaccines currently in use

mRNA vaccines (mRNA encoding the vaccine antigen is encapsulated with a lipid-based carrier, injected into the host; and then using the cellular protein translation machinery the mRNA produces the appropriate antigen which in turn provokes host immune response)

BNT162b2 BioNTech (Mainz, Germany)/Pfizer (New York, USA)

Nucleoside-modified mRNA (uridines are completely replaced by N1-methylpseudouridines), encoding the sequence of the full-length S protein with two stabilizing proline mutations in S2. It contains lipid nanoparticles (LNP) for delivery. Storage at − 70 °C. Contains 30 µg RNA

mRNA encoding the S protein, encapsulated into an LNP, enters the host cell by endocytosis. After endosomal escape into the host cytosol, the S specific mRNA is translated along ribosomes associated with the endoplasmic reticulum (ER). The newly synthesized S protein is transported into the lumen of ER (as happens in case of natural infection). Further transport occurs via exocytic pathway leading to the expression of the spike protein at the plasma membrane. The S protein is also degraded and enters the major histocompatibility complex (MHC) I and II pathways

95% (Phase III clinical trials)

Heinz and Stiasny (2021), Noor (2021a, c), Gómez et al. (2021) and Yadav et al. (2021)

mRNA-1273 (Moderna, Cambridge, MA, USA)

Nucleoside-modified mRNA (as stated above), encoding the sequence of the full-length S protein with two stabilizing proline mutations in S2. It contains LNP for delivery. Storage at − 20 °C. Contains 100 µg RNA

94.1% (Phase III clinical trials)

Heinz and Stiasny (2021), Noor (2021a, c), Gómez et al. (2021) and Yadav et al. (2021)

Adenovector vaccines (using adenoviruses as vectors based on their capacity to induce potent innate and adaptive immune responses)

Sputnik V (Gamaleya Institute in Moscow)

Number of viral particles, i.e., the human adenovirus 5 (hAd5) plus hAd26: 1 × 10¹¹ (18 µg of adenovirus protein; based on approximately 100 million amino acids composing adenovirus capsid)

Adenovector containing S gene as part of the viral DNA enters host cytosol (endocytosis). After escaping endosomal lysis, capsid migrates into the nucleus and produces S-specific mRNA transcripts. The S specific mRNA is translated in ribosomes associated with the ER, and the S protein is transported into the lumen; exocytosis occurs leading to the expression of S protein at the plasma membrane. The S protein is also degraded and enters MHC I and II pathways

91.6% (Phase III clinical trials)

Heinz and Stiasny (2021)

ChAdOx1-S/AZD1222 (University of Oxford/AstraZeneca, Cambridge, UK)

Uses a chimpanzee common cold viral vector (ChAdOx1), which delivers the code that allows the host cells to make the SARS-CoV-2 spike protein

Number of viral particles: 5 × 10¹⁰ (9 µg of adenovirus protein; based on approximately 100 million amino acids composing adenovirus capsid)

70.4% after the 1st dose and 81.3% after the 2nd dose (Phase III clinical trials)

Heinz and Stiasny (2021)

Ad26.COV2.S (Janssen Pharmaceuticals [pharmaceutical company of Johnson & Johnson], Beerse, Belgium)

The Janssen hAd26 vaccine contains stabilizing mutations similar to those engineered into the mRNA vaccines

Humoral immune responses (binding and neutralizing antibody responses), cellular immune responses (CD4⁺ and CD8⁺ T cell responses), a variety of antibody subclasses, Fc receptor binding properties, and antiviral functions were noticed

66.9% (Phase III clinical trials); another Phase III clinical trial is ongoing (NCT04436276)

Heinz and Stiasny (2021), Gómez et al. (2021) and Stephenson et al. (2021)

Inactivated whole-virus vaccine

CoronaVac/ Pi

PiCoVacc

(Sinovac Biotech, Beijing, China) and BBIBP-CorV (Sinopharm, Beijing, China)

The virus is grown in Vero cells, chemically inactivated by β-propiolactone (BPL) followed by purification; and then supplemented with adjuvants. The inactivated coronaviruses can no longer replicate although their proteins, including spike, remain intact

PiCoVacc elicited the SARS-CoV-2-specific neutralizing antibodies in mice, rats and non-human primates. The antibodies neutralized 10 representative strains. Immunizations using 3 μg or 6 μg per doses imparted partial or complete protection in macaques against viral challenge, respectively

86% (China, Bahrain, UAE); 78% (Brazil), 91.25% (Turkey), 65.3% (Indonesia)

Heinz and Stiasny (2021), Ura et al. (2021) and Gao et al. (2020)

Covaxin (Bharat Biotech, Hyderabad, Telangana, India)

The vaccine is based on an influenza virus where gene sequences from SARS-CoV-2 are inserted into M2SR-vaccine platform (M2-ion channel protein-deficient single replication)

Covaxin works by directing the immune system to elicit antibodies against the SARS-CoV-2, especially, to the so-called spike (S) proteins

India authorized Covaxin on January 2021 although no Phase III results were shown

Heinz and Stiasny (2021), Kyriakidis et al. (2021) and Corum and Zimmer (2021)

Subunit vaccine

NVX-CoV2373 (Novavax, Gaithersburg, MD, USA)

The antigenic part is a recombinant full-length S protein with stabilizing mutations produced in Sf9 insect cells. The S protein is extracted by detergent solubilization and chromatographically purified. Nanoparticles are formed by mixing the purified protein with saponin (adjuvant), cholesterol and phospholipid. Storage at 4 °C

NVX-CoV2373 S form 27.2-nm nanoparticles are thermostable and bind with high affinity to hACE2 receptor. In mice model, NVX-CoV2373 with saponin-based Matrix-M adjuvant elicit high titer anti-S IgG that blocks hACE2 receptor binding, and neutralize virus; and also induces CD4⁺ and CD8⁺ T cells, CD4⁺ follicular helper T cells (Tfh), and antigen-specific germinal center (GC) B cells in the spleen. In baboons, high titer anti-S antibodies and antigen-specific T cells were also noticed

89.1% (Phase III clinical trial in UK) and 60.1% in South Africa^a

Heinz and Stiasny (2021), Tian et al. (2021) and Wadman and Cohen (2021)

Another Phase 1/2 clinical trial is also ongoing (NCT04368988)

Tian et al. (2021)