This is the third of a series of articles that I am writing about vaccines and treatments for COVID-19. The goals are to describe progress being made in developing them. Despite the propaganda of some right-wing commentators in the USA and elsewhere, the idea of achieving herd immunity before safe and effective vaccines are available is a dangerous misconception1,2. To achieve herd immunity for COVID-19, about 70% of the population (200 million in the USA) would have to be immune. “The ability to establish herd immunity against SARS-CoV-2 hinges on the assumption that infection with the virus generates sufficient, protective immunity. At present, the extent to which humans are able to generate sterilizing immunity to SARS-CoV-2 is unclear.” 2 As of 15 July, there have been about 3.6 million coronavirus cases and 141,000 deaths3. At this rate, once 70% of the USA (population about 330 million), or 231 million people are infected, there would be about nine million deaths. Of course, if hospitals and healthcare systems become overloaded, the fatality rate will be much higher. So, developing vaccines has great priority.
As mentioned last month, three vaccine candidates are advancing into Phase 3 clinical trials. They all use a genetically engineered cold virus (Adenovirus Type 5, Ad 5) as the vector or vehicle that delivers the viral gene that codes for the spike (S) glycoprotein. This month, one of them was approved for military use in China. It is a replication defective human Ad5 vectored vaccine expressing the S protein. It successfully completed Phase 1 and 2 clinical trials4. Johnson & Johnson also have a vaccine candidate that uses a human Ad26 (type 26) vector2. One disadvantage of human adenovirus vectors is that similar adenoviruses are present in the community. As a result, many people probably have pre-existing neutralizing antibodies against the vaccine vector. In such cases, the vaccine could be neutralized before it has the chance to deliver its payload. One possible advantage of the Ad26 vector is that type 26 adenovirus is not as prevalent as Ad5. Additionally, adenovirus-based vaccines typically need refrigeration. So, thermostable vaccines are being developed that will use an adenovirus that infects sheep5. AstraZeneca and the University of Oxford are developing a vaccine based on a chimpanzee adenovirus called ChAdOx16. AstraZeneca said their total manufacturing capacity stands at two billion doses.
A more conventional approach is to make a vaccine using an inactivated SARS-CoV-2 virus. The China National Biotec Group (CNBG) has developed such a vaccine. This vaccine produced antibodies in every participant in the recently completed Phase 1/2 clinical trial. It is entering Phase 3 trials in the United Arab Emirates. In the meantime, CNBG has built a new factory for vaccines, doubling its capacity to more than 200 million doses per year7. Another Chinese vaccine developer, Sinovac, is building a factory which it hopes will be ready this year and be capable of making up to 100 million doses of vaccines per year7. The use of live attenuated or killed whole organism-based vaccines had enormous success in the control and eradication of a number of severe human infectious diseases, including smallpox, polio, measles, mumps and rubella.
The private Chinese company Sinovac Biotech is testing an inactivated vaccine called CoronaVac (formerly PiCoVacc)8. On June 13 they announced that Phase 1/2 trials on 743 volunteers found no severe adverse effects and produced an immune response. Sinovac is preparing Phase 3 trials in China and Brazil and is building a facility to manufacture up to 100 million doses annually. Vaccines made from inactivated viruses are used throughout the world with a generally excellent safety profile.
It’s also possible that repurposed vaccines could protect against SARS-CoV-2 infection and the Covid-19 disease. The Bacillus Calmette-Guerin (BCG) vaccine was developed in the early 1900s as a protection against tuberculosis. The Murdoch Children’s Research Institute in Australia is conducting a Phase 3 trial on it and several other trials are underway6-9. It has been shown to boost the innate immune system and protect against viral infections. It is thought that BCG leads to epigenetically trained populations of monocytes and/or natural killer cells. When pathogen-associated molecular patterns (PAMPs; which could be from bacteria or viruses) are detected, these innate immune cells then show an enhanced response, and eliminate the virus.
However, live attenuated virus (LAV) vaccines have potential drawbacks10. The surface antigen on the virus or other infectious organism can mutate into a form that the host’s immune system can’t recognize. As a result, it can’t defend itself. There is also a possibility that the virus could mutate and revert into a virulent form. In contrast, vaccination with nucleic acids (RNA or DNA) instead of a LAV would avoid these potential problems. Both DNA and RNA can be produced safely, quickly and in large quantities. Conventional mRNA vaccines contain mRNA from the positive strand mRNA virus (like coronaviruses). The mRNA codes for a surface protein on the virus that acts as an antigen to stimulate the host immune system so that it makes antibodies10.
Vaccines using mRNA are being developed that are tailor-made to attack the patient’s tumor11. The genetic profile of the patient’s tumor is compared to that of the same tissue from a healthy person to determine the optimal mRNA for each patient. BioNTech in Mainz, Germany has an experimental vaccine, BNT122, which has shown some remarkable success in possibly curing melanoma. Similarly, Moderna has a personalized cancer vaccine, mRNA-4157. Many people have been developing mRNA vaccines for infectious diseases, such as cytomegalovirus (CMV), which can cause neurological defects in newborns. Now, mRNA vaccines are being developed to prevent COVID-19. They use self-amplifying mRNA11. These vaccines contain mRNA that codes for a surface protein as well as a polymerase that catalyzes the production of many copies of the mRNA. So, it is self-amplifying.
Many studies on mRNA vaccines are being done. Moreover, mRNA can be easily synthesized and mass-produced10. Self-amplifying mRNA vaccines are based on an engineered viral genome containing the genes encoding an RNA polymerase and an antigenic protein, such as the S protein. However, mRNAs can form secondary structures that are recognized by innate immune receptors. This can inhibit the translation of mRNA into the desired proteins. To avoid this, modified nucleosides, such as pseudouridine and 5-methylcytosine can be incorporated into the mRNA. The innate immune receptors can’t recognize them or inhibit their translation. Self-amplifying mRNA is inserted into lipid nanoparticles (LNPs), which facilitate the delivery of mRNA and enhances antigen expression dramatically10.
Moderna has a vaccine candidate LNP-encapsulated mRNA-1273 that encodes a pre-fusion stabilized form of the S protein12. That is, the S protein undergoes a conformation change once the virus binds to the ACE2 receptor. The pre-fusion conformation is the structure that the S protein has before fusing with a human host cell. The mRNA-1273 vaccine candidate was given twice, 28 days apart. Moderna is working with Lonza to establish manufacturing suites for producing the vaccine at its facilities in the USA and Switzerland. The goal is to manufacture up to one billion doses per year for use worldwide, based on the currently expected dose of 50 micrograms (mcg) 12. In addition, clinical trials have begun at Emory University13. A Phase 1 trial began on 16 March, 2020. It has 45 healthy volunteers ages 18 to 55 years. It is expanding by enrolling an additional 60 participants: 30 adults ages 56 to 70 years and 30 adults ages 71 years and older13.
The German company BioNTech, Pfizer, and the Chinese drug maker Fosun Pharma have two LNP mRNA vaccine candidates, BNT162b1 and BNT162b214. They contain mRNA that codes for either the receptor binding domain (RBD, BNT162b1) or entire S protein (BNT162b2). They contain 1-methyl-pseudouridine mRNA (uRNA), modified nucleoside mRNA (modRNA), and self self-amplifying mRNA (saRNA). The uRNA dampens innate immune sensing and increases mRNA translation14. They were shown to be safe, well-tolerated and immunogenic in earlier trials15. They are about to enter Phase 3 clinical trials.
Imperial College London researchers have a self-amplifying mRNA vaccine candidate which produces the viral S protein in the body6. They began Phase 1/2 trials on June 15 and have partnered with Morningside Ventures to manufacture and distribute the vaccine through a new company called VacEquity Global Health6.
The American company Inovio is testing a DNA-based vaccine, INO-48006. The DNA encodes the viral S protein. In the Phase 1 trial, 94% of the participants demonstrated overall immune responses at Week 6 after two doses of INO-4800 in trial with 40 healthy volunteers. They used the same technology to develop a vaccine against the coronavirus that causes MERS. It produced nearly 100% seroconversion and neutralization from a similarly designed vaccine, INO-4700. It is the only nucleic-acid based vaccine that is stable at room temperature for more than a year and does not need to be frozen in transport or storage, which is important in mass immunizations6.
Vaccines can also contain a viral antigenic protein, such as the prefusion stabilized S glycoprotein16. Novavax has such a vaccine candidate, NVX-CoV2372. It elicited immunity in baboons and immunoprotection in mice. Purified NVX-CoV2373 S protein form 27.2 nm nanoparticles that are thermostable and bind with high affinity to the human ACE2 receptor16. It also contains a saponin-based Matrix-MTM adjuvant17. It stimulates the entry of antigen-presenting cells into the injection site and enhances antigen presentation in local lymph nodes, thus boosting immune response. Novavax plans to deliver 10 million doses of NVX CoV2373 that could be used in Phase 2/3 trials, or under an Emergency Use Authorization if approved by the FDA. They can increase that to 100 million, if needed. They have a recent history of success - a quadrivalent influenza (flu) vaccine. It met all primary objectives in its pivotal Phase 3 clinical trial in older adults17.
Injecting an antigenic protein or an mRNA that encodes such a protein hopefully will induce the production of antibodies that can protect people from COVID-19. Another approach is to use antibodies that have been produced by people who have been exposed to the SARS-CoV-2 virus. They can be isolated from the donors’ blood, then infused into patients as therapy, and possibly as a safe and effective vaccine. Not all donors are the same, nor or the antibodies that they produce. Some are more effective in protecting people from becoming infected. So, researchers evaluated the B cell repertoire of a convalescent blood donor and identified 200 antibodies that bind to several conserved sites on the S protein18. Several antibodies neutralized not just SARS-CoV-2, but also the first SARS-CoV virus and the bat SARS-like virus. They all blocked the attachment of the viruses to the ACE2 receptor. These antibodies are promising candidates for therapy and vaccines against at least three coronaviruses18.
So, antibodies targeting the S protein might produce useful vaccines19. However, it’s possible that mutations can produce antibody resistance. So, four such antibodies were developed by Regeneron. They were tested individually and when combined into cocktails. When given individually, novel escape mutants rapidly appeared, resulting in loss of effectiveness. A similar escape also happened with combinations of antibodies that were used that bind to diverse but overlapping regions of the S protein. However, escape mutants were not produced when a non-competing antibody cocktail was used. This combination of REGN10987 and REGN10933 antibodies was rationally designed to avoid escape. They bind to distinct and non-overlapping regions of the RBD. This vaccine candidate, REGN-COV2, is advancing to a Phase 3 clinical trial with 2000 subjects. Its ability to prevent infection among uninfected people who have had close exposure to a COVID-19 patient will be evaluated. They are also testing the ability of REGN-COV2 to treat hospitalized and non-hospitalized patients with COVID-196.
Progress in developing treatments
The U.S. Food and Drug Administration (FDA) had not fully approved any medication for treating people infected with the novel coronavirus, SARS-CoV-220. Still, some drug candidates are undergoing Phase 3 trials after demonstrating safety and efficacy in previous trials. For example, remdesivir is an investigational nucleotide analog with broad-spectrum antiviral activity. People taking remdesivir recovered 11 days on average, compared to 15 days for those on a placebo in a clinical trial. Acterma plus remdesivir is also in a Phase 3 trial. Acterma is an immunosuppressive drug that is already approved to treat rheumatoid arthritis. It inhibits the production of a cytokine, interleukin-6 (IL-6), which is elevated to toxic levels in a cytokine storm in COVID-19 patients. That is, immune cells release inflammatory molecules that attract more immune cells that target and kill cells that are infected with a virus, leaving a mixture of fluid and dead cells (pus) behind. This is the typical pathology of pneumonia21,22. This potentially disastrous overreaction of the immune system is known as a cytokine storm in other viral infections. The levels of interleukins IL-6 and IL-8 as well as other cytokines increase too much. Immune cells start to attack healthy tissues. Blood vessels leak, blood pressure drops, clots form, and catastrophic organ failure can occur21. Another drug for treating rheumatoid arthritis, Olumiant (baricitinib), is also in a Phase 3 trial20. Meanwhile, Dexamethasone reduced deaths in hospitalized patients with severe COVID-19 disease by one-third compared to those receiving usual care, according to the RECOVERY trial. Dexamethasone reduced fatalities by 1/3 in patients receiving invasive mechanical ventilation, and by 1/5 in patients receiving oxygen without invasive mechanical ventilation. Also, a Phase 4 clinical trial in the UK is testing ibuprofen, also known as Advil. The LIBRATE study at Kings College will evaluate the reduction in severity and progression of lung injury with three doses of ibuprofen in 230 patients with SARS-CoV-2 infections. Eli Lilly is testing a monoclonal antibody, LY-CoV555. It targets the S protein. AbbVie, Harbour BioMed, Utrecht University and Erasmus Medical Center are developing a fully human, neutralizing antibody, 47D11. Cellularity in the USA is using blood stem cells obtained from the placenta to generate natural killer cells and administer them to patients. The Russian Federation gave a temporary registration certificate for using Avifavir, an antiviral drug20. It demonstrated efficacy in treating patients diagnosed with COVID-19 disease during human clinical trials20.
At the same time, exciting new technologies are being used to produce potentially powerful treatments. CRISPR is one such technology. In a previous article, I described how CRISPR could help feed a growing population23. It has been predicted to become one of the key technologies that will be part of the fourth industrial revolution (along with artificial intelligence, robotics, nanotechnology, information technology (IT) and big data). In those applications, CRISPR would be used to edit genes to increase livestock and seafood production without the need for growth hormones or antibiotics, create better animal models of diseases, help develop improved vaccines and new prescription drug, and possibly eventually eradicate malaria. Agronomists have used CRISPR to make strains of wheat that are not affected by deadly fungi. Others produced low-gluten, nontransgenic wheat. CRISPR has also been used to increase the productivity of maize during stress caused by droughts. It can produce tomato plants and rice with much higher yields. CRISPR is a naturally-occurring defense mechanism that bacteria use to keep from being infected by viruses. To do this, bacteria use the parts of their genomes that contain base sequences that are repeated many times, with unique sequences in between the repeats. They are called “clustered regularly interspaced short palindromic repeats” or CRISPR. The second part of the defense mechanism is a set of enzymes called Cas (CRISPR-associated proteins), which can cut out the viral DNA or RNA sequence, hydrolyze it and destroy the invading viruses.
So, a new CRISPR-based antiviral strategy called PAC-MAN (Prophylactic Antiviral CRISPR in huMAN cells) targets the mRNA of the SARS-CoV-2 virus24. It was used to make CRISPR RNAs (crRNAs) that targeted either the H1N1 influenza virus or over 90% of 1087 recently sequenced coronaviruses24.
So, there are these and hundreds of other vaccine and drug candidates being developed and tested in clinical trials.
For more background on immunology, virology and COVID-19, see my previous articles in this online magazine22,25.
Glossary of Terms
Antibodies: Proteins made by immune cells that bind to antigens from a pathogen (like the spike protein in the SARS-CoV-2 virus).
Antigens: Parts of a pathogen (like the spike protein in the SARS-CoV-2 virus) that induces the production of antibodies in a host cell.
Cytokines: Chemical signaling molecules that guide a healthy immune response.
Herd immunity: “the indirect protection from infection conferred to susceptible individuals when a sufficiently large proportion of immune individuals exist in a population” 2. Epigenetics: The layer of control that lies above classical genetics. For example, the genetic code can be modified by attaching a methyl group to cytosines, thus altering transcription of the original gene.
Monoclonal antibody: An antibody made from a single clone or cell line and consisting of identical antibodies.
Monocytes: Cells in the innate immune system that can differentiate into specialized cells and affect the process of adaptive immunity. Monocytes and their progeny perform phagocytosis, antigen presentation and cytokine production.
Natural killer cells: Cells in the innate immune system that kill host (human) cells that are infected with viruses or bacteria.
PAMPs, pathogen-associated molecular patterns: Molecules that are found in viruses or bacteria that are not found in human cells.
Saponins: Amphipathic glycosides (natural detergents containing attached sugars, or glycosides). They are found in plants.
1 Dowdy, D and D’Souza, G. Early herd immunity against COVID-19: A dangerous misconception. John’s Hopkins University, 4 May, 2020.
2 Randolph, H.E. et al. Herd immunity: Understanding COVID-19. Immunity, Volume 52, pp. 737-741, 2020.
3 Worldometer, Coronavirus, 16 July, 2020.
4 Zhu, F-C et al. Safety, tolerability, and immunogenicity of a recombinant adenovirus type-5 vectored COVID-19 vaccine: a dose-escalation, open-label, non-randomised, first-in-human trial. The Lancet, Published online 22 May, 2020.
5 Castaneda, R. CanSino’s, J&J’s Covid-19 vaccines may be stifled by pre-existing antibodies while AstraZeneca’s, ReiThera’s may need booster. 23 June, 2020.
6 Corum, J. Coronavirus vaccine tracker. New York Times, 26 June, 2020.
7 Reuter’s Health News, China’s Sinopharm unit completes new COVID-19 vaccine plant, doubles capacity. 1 July, 2020.
8 Gao, Q. et al. Development of an inactivated vaccine candidate for SARS-CoV-2. Science, Volume 369, pp. 77-81, 3 July, 2020.
9 O’Neil, L.A.J. et al. BCG-induced trained immunity: can it offer protection against COVID-19?. Nature Reviews Immunology, Volume 20, pp. 335-337 (2020).
10 Zhang, C. et al. Advances in mRNA vaccines for infectious diseases. Frontiers in Immunology, Volume 10, Article 594, 2019.
11 Dolgin, E. Injection of Hope. Science, Volume 574, pp. S10-S12, 17 October, 2020.
12 Moderna gets FDA green light for COVID-19 vaccine phase II trial. ClinicalOmics, 8 May, 2020.
13 Emory News Center, Emory enrolling older adults in COVID-19 vaccine clinical trial. 17 April, 2020.
14 Kariko, K. et al. Incorporation of pseudouridine into mRNA yields superior nonimmunogenic vector with increased translational capacity and biological stability. Molecular Therapy, Volume 16, p. 1833- 1840 (2008).
15 Mulligan, M. et al. Phase 1/2 study to describe the safety, tolerability, immunogenicity, and potential efficacy of RNA vaccine candidate (BNT162b1) against COVID-19 in healthy adults. medRxiv preprint, 1 July, 2020.
16 Tian J-H. et al. SARS-CoV-2 spike glycoprotein vaccine candidate NVX-CoV2373 elicits immunogenicity in baboons and protection in mice. bioRxiv preprint 30 June, 2020.
17 Novavax Wins $1.6B in “Warp Speed” Funding; Plans First 100M Doses of COVID-19 Vaccine. Genetic Engineering & Biotechnology News, 7 July, 2020.
18 Wec, A.Z. et al. Broad neutralization of SARS-related viruses by human monoclonal antibodies. Science, 15 June 2020.
19 Baum, A. et al. Antibody cocktail to SARS-CoV-2 spike protein prevents rapid mutational escape seen with individual antibodies. Science, preprint, DOI: 10.1126/science.abd0831, 15 June, 2020.
20 Corona Virus Today, COVID-19 treatments. 15 July, 2020.
21 Wadman, M. A Rampage through the dody. Science, Volume 368, pages 356-360, 2020.
22 Smith, R.E. Developing tests, vaccines and treatments for COVID-19. Wall Street International, 24 May, 2020.
23 Smith, R.E. Using CRISPR gene editing to create new foods. An important part of the fourth Industrial Revolution. Wall Street International, 24 May, 2019.
24 Abbott, T.R. et al. Development of CRISPR as an antiviral strategy to combat SARS-CoV-2 and influenza. Cell, Volume 181, pp. 865-876, 2020.
25 Smith, R.E. Developing vaccines and treatments for COVID-19. Humans are not the enemy. Wall Street International, 24 May, 2020.