Understand how different Vaccine technologies work with the immune system to provide protection
Below are some of helpful articles that aided me in understanding how different Vaccine technologies work with the immune system to provide protection
A coronavirus disease 2019 (COVID-19) vaccine can help you develop immunity to SARS-CoV-2, the virus that causes COVID-19, without getting ill. But how exactly do the different types of COVID-19 vaccines work?
Vaccines prompt an immune response so that your body remembers how to fight a virus in the future. Some vaccines use a whole virus to cause your immune system to respond. Other vaccines use parts of the virus or genetic material that provides instructions for making specific proteins like those in the virus.
Many COVID-19 vaccines involve a spikelike structure on the surface of the COVID-19 virus called an S protein. The S protein helps the virus get inside your cells and start an infection.
Manufacturers around the world are working on different types of vaccines. The main types of COVID-19 vaccines currently available in the U.S. or in large-scale clinical trials include:
· Messenger RNA (mRNA) vaccine. This type of vaccine uses genetically engineered mRNA to give your cells instructions for how to make a harmless piece of the S protein found on the surface of the COVID-19 virus. After vaccination, your immune cells begin making the S protein pieces and displaying them on cell surfaces. This causes your body to create antibodies. If you become infected with the COVID-19 virus, these antibodies will fight the virus.
After the mRNA helps your cells make the protein pieces, the mRNA is immediately broken down. It never enters the nucleus of your cells, where your DNA is kept. Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use mRNA.
· Vector vaccine. In this type of vaccine, genetic material from the COVID-19 virus is inserted into a different kind of weakened live virus, such as an adenovirus. The weakened virus (viral vector) serves as a delivery system. When the viral vector gets into your cells, it delivers genetic material from the COVID-19 virus that gives your cells instructions to make copies of the S protein. Once your cells display the S proteins on their surfaces, your immune system responds by creating antibodies and defensive white blood cells. If you become infected with the COVID-19 virus, the antibodies will fight the virus.
Viral vector vaccines can't cause you to become infected with the COVID-19 virus or the viral vector virus. Also, the genetic material that's delivered doesn't become part of your DNA. The Janssen/Johnson & Johnson COVID-19 vaccine is a vector vaccine. AstraZeneca and the University of Oxford are also working on a vector COVID-19 vaccine.
· Protein subunit vaccine. Subunit vaccines include only the parts of a virus that best stimulate your immune system. This type of COVID-19 vaccine contains harmless S proteins. Once your immune system recognizes the S proteins, it creates antibodies and defensive white blood cells. If you become infected with the COVID-19 virus, the antibodies will fight the virus.
Novavax is working on a protein subunit COVID-19 vaccine.
The U.S. Food and Drug Administration has given emergency use authorization to the Pfizer-BioNtech, Moderna and Janssen/Johnson & Johnson COVID-19 vaccines. However, the FDA and the Centers for Disease Control and Prevention have recommended a pause in distributing the Janssen/Johnson & Johnson vaccine due to rare blood clotting reactions in a small number of people who have gotten the vaccine. More types of vaccines are expected to be authorized for use in the coming months.
A COVID-19 vaccine might prevent you from getting COVID-19 or from becoming seriously ill or dying due to COVID-19. Consult your local health department for the latest information on how and when you can receive a vaccine.
DEAD OR DISABLED VIRUSES
Traditional vaccines contain a dead or disabled virus, designed to be incapable of causing severe disease while also provoking an immune response that provides protection against the live virus.
1. Live-attenuated viruses
Attenuated means 'weakened'. Weakening a
live virus typically involves reducing its virulence — capacity to cause
disease — or ability to replicate through genetic engineering. The virus still
infects cells and causes mild symptoms. For a live-attenuated virus, an obvious
safety concern is that the virus might gain genetic changes that enable it to
revert back to the more virulent strain. Another worry is that a mistake during
manufacturing could produce a defective vaccine and cause a disease outbreak,
which once happened with a polio vaccine.
But using a live-attenuated virus has one huge benefit: vaccination resembles natural infection, which usually leads to robust immune responses and a memory of the virus' antigens that can last for many years.Live-attenuated vaccines based on SARS-CoV-2 are still undergoing preclinical testing, developed by start-up Codagenix and the Serum Institute of India.
2. Inactivated viruses
Inactivated means 'dead' ('inactivated' is used because some scientists don't consider viruses to be alive). The virus will be the one you want to create a vaccine against, such as SARS-CoV-2, which is usually killed with chemicals.Two Chinese firms have developed vaccines that are being tested for safety and effectiveness in large-scale Phase III clinical trials: 'CoronaVac' (previously 'PiCoVacc') from Sinovac Biotech and 'New Crown COVID-19' from Sinopharm. Both drugs contain inactivated virus, didn't cause serious adverse side-effects and prompted the immune system to produce antibodies against SARS-CoV-2.Sinopharm's experimental vaccine has reportedly been administered to hundreds of thousands of people in China, and both drugs are now being trialled in countries across Asia, South America and the Middle East.
COVID-19 vaccine landscape (left) and platforms for SARS-CoV-2 vaccine development (right) The global COVID-19 vaccine landscape (left) and Vaccine platforms used for SARS-CoV-2 vaccine ... [+] Springer
Artificial vectors. Another conventional approach in vaccine design is to artificially create a vehicle or 'vector' that can deliver specific parts of a virus to the adaptive immune system, which then learns to target those parts and provides protection. That immunity is achieved by exposing your body to a molecule that prompts the system to generate antibodies, an antigen, which becomes the target of an immune response. SARS-CoV-2 vaccines aim to target the spike protein on the surface of coronavirus particles — the proteins that allows the virus to invade a cell.
3. Recombinant viruses
A recombinant virus is a vector that combines the target antigen from one virus with the 'backbone' from another — unrelated — virus. For SARS-CoV-2, the most common strategy is to put coronavirus spike proteins on an adenovirus backbone.Recombinant viruses are a double-edged sword: they behave like live-attenuated viruses, so a recombinant vaccine comes with the potential benefits of provoking a robust response from the immune system but also potential costs from causing an artificial infection that might lead to severe symptoms.A recombinant vaccine might not provoke an adequate immune response in people who have previously been exposed to adenoviruses that infect humans (some cause the common cold), which includes one candidate developed by CanSino Biologics in China and 'Sputnik V' from Russia's Gamaleya National Research Centre — both of which are in Phase III clinical trials and are licensed for use in the military. To maximize the chance of provoking immune responses, some vaccines are built upon viruses from other species, so humans will have no pre-existing immunity. The most high-profile candidate is 'AZD1222', better known as 'ChAdOx1 nCoV-19' or simply 'the Oxford vaccine' because it was designed by scientists at Oxford University, which will be manufactured by AstraZeneca. AZD1222 is based on a chimpanzee adenovirus and seems to be 70% effective at preventing Covid-19. Some recombinant viruses can replicate in cells, others cannot — known as being 'replication-competent' or 'replication-incompetent'. One vaccine candidate that contains a replicating virus, developed by pharmaceutical giant Merck, is based on Vesicular Stomatitis Virus (VSV), which infects guinea pigs and other pets.
4. Virus-like particles
A virus-like particle, or VLP, is a structure assembled from viral proteins. It resembles a virus but doesn't contain the genetic material that would allow the VLP to replicate. For SARS-CoV-2, the VLP obviously includes the spike protein.One coronavirus-like particle (Co-VLP) vaccine from Medicago has passed Phase I trials to test it's safe and has entered Phase II to test that it's effective.While there are currently few VLPs being developed for Covid-19, the technology is well-established and has been used to produce commercial vaccines against human papillomavirus (HPV) and hepatitis B. Viral components. All vaccines are ultimately designed to expose the immune system to parts of a virus, not the whole thing, so why not deliver just those parts? That's the reasoning behind vaccines that only contain spike proteins or spike genes.
5. Proteins
Protein-based vaccines can consist of the full-length spike protein or the key part, the tip of the spike that binds the ACE2 receptor on the surface of a cell — ACE2 is the lock that a coronavirus picks in order to break into the cell. Manufacturing vaccines containing the protein alone has a practical advantage: researchers don't have to deal with live coronaviruses, which should be grown inside cells within a biosafety level-3 lab. A vaccine against only part of the protein — a 'subunit' — will be more vulnerable to being rendered useless if random mutations alter the protein, known as 'antigenic drift', but full-length proteins are harder to manufacture. The immune system can recognize either as an antigen. One candidate vaccine based on protein subunits is 'NVX-CoV2373' from Novavax, where the spike subunits are arranged as a rosette structure. It's similar to a vaccine that's already been licensed for use, FluBlok, which contains rosettes of protein subunits from the influenza virus.
6. Nucleic acids
Nucleic-acid vaccines contain genetic material, either deoxyribonucleic acid or ribonucleic acid — DNA or RNA. In a coronavirus vaccine, the DNA or RNA carries genetic instructions for producing a spike protein, which is made within cells. Those spike genes can be carried on rings of DNA called 'plasmids', which are easy to manufacture by growing them in bacteria. DNA provokes a relatively weak immune response, however, and can't simply be injected inside the body — the vaccine must be administered using a special device to force DNA into cells. Four DNA-based candidates are in Phase I or II trials. The two most famous nucleic-acid vaccines are the drugs being developed by pharmaceutical giant Pfizer, partnered with BioNTech, and Moderna. Pfizer's 'BNT162b2' and Moderna's 'mRNA-1273' both use 'messenger RNA' — mRNA — to carry the spike genes and are delivered into cells via a lipid nanoparticle (LNP). The two mRNA vaccines have completed Phase III trials and preliminary results suggests they're over 90% effective at preventing Covid-19.
As the above examples show, not only there are many potential vaccines but also various approaches. And while some technologies have already provided promising results, it remains to be seen which will actually be able to defeat the virus.
https://www.forbes.com/sites/jvchamary/2020/11/29/coronavirus-vaccines-difference/?sh=4bac30dc2ae6
Inactivated vaccines use a "killed" version of the virus, which is treated with UV light or chemicals so that it cannot cause disease. The killed virus is then introduced into the body so that its antigens (the components that stimulate the immune system) will trigger an immune response. This method is also used in vaccines that combat polio and rabies. Inactivated vaccines are typically not as strong as live vaccines, so typically, several doses are needed over time. This is why some vaccines are administered with an initial dose, followed by booster shots later on.
Further Readings
https://www.who.int/news-room/feature-stories/detail/the-race-for-a-covid-19-vaccine-explained
https://www.mayoclinic.org/coronavirus-covid-19/vaccine/comparing-vaccines
https://www.yalemedicine.org/news/covid-19-vaccine-comparison
https://www.forbes.com/sites/jvchamary/2020/11/29/coronavirus-vaccines-difference/?sh=4bac30dc2ae6
https://www.webmd.com/vaccines/covid-19-vaccine/news/20201214/closer-look-at-three-covid-19-vaccines
https://www.webmd.com/vaccines/covid-19-vaccine/news/20201214/closer-look-at-three-covid-19-vaccines
https://www.theguardian.com/world/2021/jan/31/whats-the-difference-between-all-the-covid-vaccines
https://www.theguardian.com/world/2021/jan/31/whats-the-difference-between-all-the-covid-vaccines
https://www.huffpost.com/entry/how-covid-vaccines-compare_l_60186e8fc5b6aa4bad36a3b0
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