It cannot be said that one vaccine strategy is better than the other. Over time we may have enough data to make such comparisons. From a biological perspective, the advantage of mRNA-based vaccines, such as Pfizer or Moderna, is that the mRNA is in the liposome, not in the viral vector, and the mRNA has a short life and action in the host cell. The mRNA along with the liposome will move into the host cell. It will recognize the ribosome in the cytoplasm instead of the nucleus. This would create a protein that resembles the spike protein of SARS-CoV-2. It will be sent to the host cell’s plasma membrane.
The immune system will observe this protein and the immune response will be generated. The immune system will generate memory so that it can be dealt with later if SARS-CoV-2 infection occurs. This sequence is definite and the mRNA vaccine is unlikely to remain in the genetic material host cell for long. One problem with this type of vaccine may be that higher doses have to be taken for complete protection. Government officials say that it will be approved in India soon and it can be expected to come to India by July.
Apart from this, in the case of adenoviral vector vaccines, they have to enter the nucleus of the host cell, only then will their action take place. Genetic material is in the genome of the vector from which the mRNA is formed in the nucleus of the host cell. The process ahead is similar to that of the mRNA vaccine. In this too, a virus-like spike protein will be formed, which the immune system will recognize and produce a response.
If any other adenovirus infection has occurred earlier, then only immune response can be generated against the viral vector, which can cause the vaccine to fail. To avoid this, Oxford-AstraZeneca has used the chimpanzee vector instead of the human vector. There are concerns in many countries about the side-effects of Kovishield, but experts say it has more to do with its impact against Kovid-19 than any threat.
Unlike these two, Indo-Biotech-made Covaxin has used the inactivated SARS-CoV-2 virus. This vaccine has been created by the Indian Council of Medical Research and the National Institute of Virology. This strategy has been used previously in seasonal influenza vaccines. Inactivated bacteria are also used in these.
Its biggest advantage may be that it not only produces immune responses after recognizing the spike protein of SARS-CoV-2, but can also identify other parts of the virus. However, inactivated vaccines also initially cause low immune response. That is why it may require even more dosages.
Russia’s Sputnik V vaccine has also been approved in India. It is made from cold-type viruses. This virus is engineered to eliminate the risk of it and then a part of the corona virus is transported into the body using it as a carrier. The immune system recognizes the virus’s genetic code and fights it without falling ill. This creates special antibodies against the corona virus in the body. The special thing is that the first and second doses of Sputnik use different vectors. Researchers say that using different vectors, the immune response is stronger and longer lasting.
Initially, the third phase of trial data was disputed. However, it has been approved in India. Mild side effects have been reported from this vaccine.