Covaxin elicits immune memory to virus

Covaxin elicits immune memory to virus

Context: A small study conducted on 71 individuals who received two doses of Covaxin found that the vaccine generates antibodies and easily detectable memory B cell and T cell responses in many recipients.

• According to the study by National Institute of Immunology the immunological memory to the virus and the variants after full vaccination seemed to last up to six months in many individuals.
• Even though antibodies may decline with time, the memory compartment will be marshalled quickly in case of a future infection to limit virus multiplication and disease.
• This shows that immune system can respond swiftly and provide protection in case of a breakthrough infection.
• The study shows that the quantity of memory T cells is comparable to that of natural infection, and the composition of memory subsets is indicative of a long-term durability of vaccine-induced T cell responses.

Immunity

The immune system is a network of intricately connected cells to protect the body from internal and external threats. It is broadly classified into two sub-types: innate (or natural) and adaptive (or acquired). The key differences between the two are the specificity and agility of the responses generated towards a perceived threat.

Because of the intricate nature of the immune system, the innate system also provides cues in the forms of chemical signals (cytokines) or degraded products of infectious organisms (antigens) to activate the adaptive immune system, using a process known as “antigen presentation”. Without these cues, the adaptive immune system cannot be activated.

The adaptive immune system has evolved to provide a more versatile and highly target-specific defence with an ability to distinguish very subtle differences in the make-up of infectious agents. But the adaptive immune system is slow and can take several days before two key cell types – B cells and T cells – are brought into play.

T cells are further grouped into two sub-types, CD4+ and CD8+ cells. CD4+ are helper T cells that help the activity of other immune cells by releasing cytokines. The cytokines prime the maturation of B cells, which become plasma cells and produce antibodies to neutralise the pathogen. CD8+ cytotoxic T cells, on the other hand, directly kill infected cells.

Once the adaptive immune system has vanquished the invader, a pool of long-lived memory T and B cells are made. These memory lymphocytes remain dormant until the next time they encounter the same pathogen. This time, though, they produce a much faster and stronger immune reaction. Memory is the key feature of the adaptive immune system, enabling long-term protection.

T cells and B cells in COVID-19

Since most people have not been exposed to the novel coronavirus, it can safely be assumed that uninfected people have no memory T and B cells and therefore no protection from a COVID-19 infection. Technically speaking, as with any other infection, COVID-19 should generate an immune response, priming the proliferation of anti-COVID T and B cells.