In India, the work of vaccinating the population to combat the corona virus continues at a tremendous pace. India’s Covaxin is not only on the ground, Oxford-AstraZeneca’s Covishield is also at the forefront of this battle. Apart from those two, the option of installing Russia’s Sputnik V also presented itself and in a few weeks the doors to India will also be able to open for BioNTech-Pfizer’s vaccine. In such a situation, it becomes important for people to understand which vaccine to choose and why. To understand this, Shatakshi Asthana for Navbharat Times Online spoke with Dr. Joseph Roche, a fellow of the American Physiological Society, who explained in detail how all of these vaccines differ from each other.
At present, it cannot be said that one vaccine strategy is better than another. Over time, we may have enough data to make such comparisons. From a biological point of view, the advantage of mRNA-based vaccines, such as Pfizer or Moderna, is that the mRNA is contained in the liposomes, not the viral vector, and the mRNA has a duration of shorter life and action in the host cell. The mRNA as well as the liposomes will travel to the host cell. It will be recognized by the ribosomes in the cytoplasm instead of the nucleus. This will create a protein similar to the SARS-CoV-2 spike protein. It will be sent to the plasma membrane of the host cell.
The immune system will see this protein and an immune response will be generated. The immune system will create a memory so that it can be processed later in the event of a SARS-CoV-2 infection. This sequence is fixed and the genetic material of the mRNA vaccine is unlikely to stay in the host cell for long. A problem with this type of vaccine may be that high doses must be taken for full protection. Government officials say it will be approved in India soon and is expected to arrive in India by July.
In the case of adenoviral vector vaccines, on the other hand, they must enter the nucleus of the host cell for their action to take place. The genetic material is contained in the genome of the vector from which mRNA is made in the nucleus of the host cell. The upcoming process is the same as that of the mRNA vaccine. In this case too, a spike protein like a virus will be formed, which the immune system will recognize and generate a response.
If there has been an infection with another adenovirus before, an immune response may be generated against the viral vector itself, which may cause the vaccine to fail. To avoid this, Oxford-AstraZeneca used the chimpanzee vector instead of the human vector. Side effects from Kovidshield are cause for concern in many countries, but experts say it benefits more from its effect against Kovid-19 than from any danger that comes with it.
Unlike these two, the inactivated SARS-CoV-2 virus was used in Covaxin manufactured by Bharat-Biotech. This vaccine was jointly manufactured by the Indian Council for Medical Research and the National Institute of Virology. This strategy has been used before, as in the seasonal flu vaccine. In this case, inactivated bacteria are also used.
Its biggest advantage might be that it not only generates an immune response after recognizing the SARS-CoV-2 spike protein, but can also identify itself based on other parts of the virus. However, inactivated vaccines also produce a weak immune response initially. Therefore, even larger doses may be needed.
The Russian vaccine Sputnik V has also been approved in India. It is made from cold type viruses. The threat is eliminated by designing this virus and then using it as a vector, part of the corona virus is delivered to the body. The immune system recognizes the genetic code of the virus and fights it without getting sick. For this reason, special antibodies are made in the body against the corona virus. The peculiarity is that different vectors are used in the first and second doses of Sputnik. Researchers say that using different vectors makes the immune response stronger and longer lasting.
Initially, there had been a dispute over the test data of the third phase. However, it was approved in India. Mild side effects have been reported with this vaccine.