|I know that there are several vaccines for Covid19 so far, from different labs and countries. Are all of them mRNA or DNA vaccines? Are any of them using the attenuated virus like the conventional vaccines? |
|Question Date: 2021-04-02|
There 4 are types of vaccines right now. The first three are based either on RNA (the Pfizer and Moderna), or DNA (Johnson and Johnson, Oxford/Astrazeneca and Sputnik V) or are inactivated (Sinopharm, SinoVac and Bharat). So attenuated means that you are given a live virus that has been weakened. The virus infects you, but usually replicates too slowly for you to get sick, but it is alive. So you are actually infected, and this allows the immune system to 'see' the virus and respond.
An inactivated virus is one that has been grown in a dish, and then is killed (either chemically or it is heated up). The killed virus is injected, and again the immune system can 'see' it and respond. When I say 'see' it, you are creating tags (called antibodies) that bind specifically to parts of the virus, and when you have those antibodies in your blood, this can block or really slow down a virus from infecting a cell.
The RNA and DNA vaccines are directing your cells to make just one part of the virus, called the Spike. When that happens, your immune system recognizes this and makes antibodies to the Spike. The last vaccine, called Novavax, is really cool. It is just the Spike stuck onto these small beads, called nanoparticles. When they are injected into your arm, your immune system recognizes this and makes antibodies. So anyway, here's the deal. If you are infected with the virus, it gets into cells, copies itself, and makes a bunch of Spike. Your immune system recognizes this and makes antibodies to Spike. The RNA and DNA vaccines are telling making your cells just make the Spike, without any other part of the virus. The inactivated and nanoparticles are basically dead Spike that has already been made. The goal of the vaccines is to allow the immune system to see and respond to the covid Spike in a safe way, so that the antibodies are already made if you ever get infected..
Only 2 of the 5 major COVID-19 vaccines use mRNA. The others use approaches which are the same as those used for many vaccines in the past, which I suppose makes them more "conventional vaccines". None of them use an attenuated version of the COVID-19 virus itself, and one does not use a full version of any virus at all.
The Pfizer/BioNTech and Moderna vaccines use mRNA. Vaccines of this type use pieces of genetically engineered mRNA to instruct your immune system cells to make and display a harmless part of the virus. Your immune system then makes antibodies which recognize this piece of the virus (in particular for COVID-19, an S protein from the surface of the virus) and white blood cells will attack the real virus if one becomes infected. COVID-19 is the first virus for which mRNA vaccines have been given approval.
The Janssen/JNJ and Astra-Zeneca/Univ. Oxford vaccines are viral vector type vaccines. Viral vector vaccines essentially use a weak virus to carry genetic material from the "real" virus to the body. Like the mRNA vaccines, once the immune system sees this genetic material, they begin to display a protein of the real virus (again, for COVID-19 this is an S protein from the surface) and then can make antibodies to defend against it. Viral vector vaccines have been used for Ebola, Zika, and the flu, among others.
The Novavax vaccine is a subunit vaccine. Unlike the previous types which rely on the body to make a piece of the virus within the patient, subunit vaccines contain pieces of the virus, such as a protein or sugar found in/on the virus (and only pieces, not the full virus). The preferred subunits are those which trigger the strongest immune response. Subunit vaccines have been developed for protection against Hepatitis B, whooping cough, shingles, and more. These may also be referred to as recombinant, polysaccharide, or conjugate vaccines.
Other vaccine technologies also exist. As in the question, some vaccines use attenuated (weakened) versions of the virus to generate the immune response. The germ could be either reduced in strength or completely killed/inactivated. These types of vaccines are used to protect against polio, rabies, measles, and smallpox. Toxoid vaccines use a product of the virus to stimulate the immune system. These are used when it is a harmful compound made by the virus which causes the disease. The immune response is then directed at that toxic product rather than the virus which makes it. These vaccines are used for diptheria and tetanus.
None of the vaccines currently available in the US are DNA vaccines. There are also no attenuated virus vaccines.
The Moderna and Pfizer/BioNTech vaccines are mRNA vaccines. The Johnson & Johnson vaccine, rather than using an attenuated coronavirus is based on a human adenovirus that has been modified to contain the gene for making the spike protein of the SARS-CoV-2 virus that causes COVID-19.
So far there are 13 vaccines that have been approved for use in humans in at least one country. The 3 major vaccines in the US are either mRNA vaccines (pfizer and moderna) or a viral vector vaccine which delivers DNA (Johnson & Johnson). Your cells use the nucleic acid delivered by these vaccines to make viral proteins, which the body will mount an immune response against without experiencing any infection. Outside of the US, inactivated coronavirus vaccines have been approved for use in humans. Inactivated vaccines are virus particles that have been grown in labs then somehow inactivated so they can't cause infection at all. When the body is exposed to these inactive particles they will still mount an immune response against the foreign protein on the outside of the particle even though it cannot infect cells.
Inactive virus vaccines are different from attenuated viral vaccines in that attenuated viruses are unable to cause serious infections but still have some biological activity, whereas inactive vaccines are completely "dead" viral particles. Finally there are also viral protein subunit vaccines against coronavirus that are also approved in other countries. These vaccines use a single, small piece of a virus protein to produce an immune response by the body.
There are still 100s of other vaccines in development all around the world, with dozens currently in clinical trials in humans. While no live, attenuated coronavirus vaccine has been approved for use yet, there are vaccines in development that utilize the technology.
According to this page by the World Health Organization (part of the United Nations), there are over 200 COVID vaccines in development and over 50 in human trials. The site also has a nice explanation of the general approaches. Not all “conventional” vaccines use attenuated viruses.
The AstraZeneca vaccine is the attenuated kind. It’s being used in Europe. The common COVID vaccines in the US all use nucleic acids. Moderna and Pfizer use RNA. Johnson & Johnson uses DNA.
One of the major concerns in the development of a vaccine is the balance of safety vs. efficacy (how well it works). This cannot just be calculated because humans think about harm caused by an action differently than harm caused by inaction. Say that a disease were deadly 5% of the time and the risk of getting the disease were 50%. That would mean that everyone in the population had a 2.5% chance of dying of the disease. Would it be acceptable to give people a vaccine that gave 100% protection, but was lethal 2% of the time? Most people would say no, even though mathematically they’d be better off being vaccinated.
That’s vaccines are required to be highly effective and very safe, so that most people have few or no side effects at all and the risk of death is extremely small. Since nothing is 100% safe, what do you think the proper balance is between safety and efficacy?
Thanks for asking,
Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use mRNA .
The main types of COVID-19 vaccines currently available in the U.S. or in large-scale clinical trials include:
• Messenger RNA (mRNA) vaccine.
• 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 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.
types of vaccines.
There are several different types. The Pfizer and Moderna are RNA vaccines, the AstraZeneca is an adenovirus-DNA vaccine, and the Chinese and Indian vaccines use deactivated strains of the Covid-19 virus (which is an RNA virus).
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