Covishield –
This vaccine produces antibodies against only a specific region of the virus. It contains a portion of the DNA that codes for the spike protein (S-protein). Once inside the cells, the DNA part first needs to enter the nucleus to create its mirror image (complementary RNA). Then this RNA comes out in the cytoplasm as a messenger and starts making S-protein through a machine available for this purpose called ribosome. Since it is S-protein that provokes immunity it may not be as close to natural immunity as created by Covaxin. If there are any long-term side effects of the DNA material remaining inside the nucleus (e.g. integration in human DNA) is not yet known. So far, DNA vaccines were only being tried out for treating cancer patients and never used for preventing infections in normal subjects.
Covaxin –
This vaccine can produce antibodies against many regions of the complete virus. Since this vaccine contains a full inactivated virus with all its 29 proteins intact, the immunity provoked by it will be more comprehensive and closer to natural immunity arising out of an infection. This does not contain any genetic material that can either replicate or go inside the nucleus but provokes the immunity against virulent proteins other than S-protein as well. This uses a tried and tested technology platform used by other vaccines like polio vaccine. However, these vaccines require an adjuvant to provoke immunity. For this purpose, alum is commonly used which mainly provokes Th-2 type immunity which also leads to more side effects. Hence, Bharat Biotech has used an alternative adjuvant “Algel-IMDG (Imidazoquinolinone)” which stimulates Th-1 type immunity that is also generated by mRNA/DNA vaccines.
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