Why we chose Oxford vaccine over others?
To understand how COVID-19 vaccines work, it helps to first look at how our bodies fight illness. When germs, such as the virus that causes COVID-19, invade our bodies, they attack and multiply. This invasion, called an infection, is what causes illness. Our immune system uses several tools to fight infection. Blood contains red cells, which carry oxygen to tissues and organs, and white or immune cells, which fight infection. Different types of white blood cells fight infection in different ways.
Macrophages are white blood cells that swallow up and digest germs and dead or dying cells. The macrophages leave behind parts of the invading germs called antigens. The body identifies antigens as dangerous and stimulates antibodies to attack them. B-lymphocytes are defensive white blood cells. They produce antibodies that attack the pieces of the virus left behind by the macrophages. T-lymphocytes are another type of defensive white blood cell. They attack cells in the body that have already been infected.
The first time a person is infected with the virus that causes COVID-19, it can take several days or weeks for their body to make and use all the germ-fighting tools needed to get over the infection. After the infection, the person's immune system remembers what it learned about how to protect the body against that disease. The body keeps a few T-lymphocytes, called memory cells that go into action quickly if the body encounters the same virus again. When the familiar antigens are detected, B-lymphocytes produce antibodies to attack them. Experts are still learning how long these memory cells protect a person against the virus that causesCOVID-19.
There are more vaccine candidates simultaneously in the pipeline for COVID-19 than ever before for an infectious disease. All of them are trying to achieve the same thing immunity to the virus, and some might also be able to stop transmission. They do so by stimulating an immune response to an antigen, a molecule found on the virus. In the case of COVID-19, the antigen is typically the characteristic spike protein found on the surface of the virus, which it normally uses to help it invade human cells. There are four categories of vaccines in clinical trials: whole virus, protein subunit, viral vector and nucleic acid (RNA and DNA). Some of them try to smuggle the antigen into the body, others use the body's own cells to make the viral antigen.
Many conventional vaccines use whole viruses to trigger an immune response. There are two main approaches. Live attenuated vaccines use a weakened form of the virus that can still replicate without causing illness. Inactivated vaccines use viruses whose genetic material has been destroyed so they cannot replicate, but can still trigger an immune response. Both types use well-established technology and pathways for regulatory approval, but live attenuated ones may risk causing disease in people with weak immune systems and often require careful cold storage, making their use more challenging in low-resource countries. Inactivated virus vaccines can be given to people with compromised immune systems but might also need cold storage.
Nucleic acid vaccines use genetic material either RNA or DNA to provide cells with the instructions to make the antigen. In the case of COVID-19, this is usually the viral spike protein. Once this genetic material gets into human cells, it uses our cells' protein factories to make the antigen that will trigger an immune response. The advantages of such vaccines are that they are easy to make and cheap. Since the antigen is produced inside our own cells and in large quantities, the immune reaction should be strong. A downside, however, is that so far, no DNA or RNA vaccines have been licensed for human use, which may cause more hurdles with regulatory approval.
Also, RNA vaccines need to be kept at ultra-cold temperatures, -70C or lower, which could prove challenging for countries that don't have specialised cold storage equipment, particularly low-and middle-income countries. Pfizer/BioNTech and Moderna vaccine, nucleic acid vaccine, contains a segment of the SARS-COV-2 virus genetic material that codes for a specific protein. The genetic material can be DNA or RNA. Our cells use the genetic material to make the SARS-COV-2 protein, which is recognised by the immune system to trigger a response.
Viral vector vaccines also work by giving cells genetic instructions to produce antigens. But they differ from nucleic acid vaccines in that they use a harmless virus, different from the one the vaccine is targeting, to deliver these instructions into the cell. One type of virus that has often been used as a vector is adenovirus, which causes the common cold. As with nucleic acid vaccines, our own cellular machinery is hijacked to produce the antigen from those instructions, to trigger an immune response. Viral vector vaccines can mimic natural viral infection and should therefore trigger a strong immune response.
However, since there is a chance that many people may have already been exposed to the viruses being used as vectors, some may be immune to it, making the vaccine less effective. Viral vector vaccine uses an unrelated harmless virus that has been modified to act as a delivery system to carry genetic material that codes for specific SARS COV -2 protein. The delivery virus is known as the viral vector. Our cells use the genetic material to make the SARS-Cov-2 protein which is recognised by the immune system to trigger a response.
The University of Oxford/AstraZeneca the vaccine uses this technology to protect against COVID-19. This type of vaccine uses an unrelated harmless virus (the viral vector) to deliver SARS-CoV-2genetic material. When administered, our cells use the genetic material to produce a specific viral protein, which is recognised by our immune system and triggers a response. This response builds immune memory, so your body can fightoff the virus in future. Protein subunit vaccines include harmless pieces (proteins) of the virus that causeCOVID-19 instead of the entire germ.
Once vaccinated our immune system recognizes that the proteins don't belong in the body and begins making T-lymphocytes and antibodies. If we are ever infected in the future, memory cells will recognize and fight the virus. The coronavirus vaccine developed by the University of Oxford is highly effective at stopping people developingCovid-19 symptoms, a large trial shows. Interim data suggests 70% protection, but the researchers say the figure may be as high as 90% by tweaking the dose.
Pfizer and Moderna vaccines showed 95%protection. However, the Oxford jab is far cheaper and is easier to store and get to every corner of the world than the other two. So the vaccine will play a significant role in tackling the pandemic. It uses a completely different approach to the vaccines from Pfizer and Moderna, which inject part of the virus's genetic code into patients. The Oxford vaccine is a genetically modified common cold virus that used to infect chimpanzees.
It has been altered to stop it causing an infection in people and to carry the blueprints for part of the coronavirus, known as the spike protein. Once these blueprints are inside the body they start producing the coronavirus' spike protein, which the immune system recognizes as a threat and tries to squash it. Lastly, the cold chain system and low cost, will be better serve our purpose in case of oxford vaccine, give a thin edge over others.
Dr Zubair Khaled Huq is Family Medicine, Gerontology, Public