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Immunity protects the human body from any type of infection caused by pathogens. Immunity is categorized as Active immunity or passive immunity. Active immunity develops when the body comes in contact with a disease-causing pathogen and produces antibodies for fighting against the disease or the invading cause. Exposure to the disease organism maybe by actually being infected by the diseases which produce in natural immunity or by vaccination called vaccine-induced immunity. This helps the immune system of the body recognize the infection and produce the antibodies needed to fight it. Hence, active immunity is long-lasting, and sometimes life-long. 1
The long-lasting immune protection involves different components including antibodies that circulate in the blood, recognizes the pathogens like viruses and fight against them. Different types of T cells help recognize and kill pathogens. B cells make new antibodies when the body needs them. 2
A long-lasting immunity is essential to be protected from infectious diseases like the current COVID-19. The SARS-CoV-2 virus is responsible for causing COVID-19 and spreads easily. SARS-CoV-2 belong to Coronavirus family which causes illness such as the common cold, severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS). 3
The genome of coronavirus comprises ∼30000 nucleotides encoding four protein structures namely Nucleocapsid (N) protein, Membrane (M) protein, Spike (S) protein and Envelope (E) protein and several non-structural proteins (nsp). The capsid is the protein shell, inside which is the nuclear capsid or N-protein which is bound to the virus single positive-strand RNA that allows the virus to attack human cells and plays a vital role in its replication and transcription increasing the spread of the infection. The S-protein present over the surface of the virus causes the virus to attach to the host cell surface receptors helping the virus to enter the host cell. 3
A study in the UK states that the magnitude of the adaptive immune response to SARS-CoV-2 was significantly increased among children (aged 3 to 11 years), compared to among adults. The study also stated that SARS-CoV-2 infection among children doubled antibody titers against four other types of human coronaviruses that frequently cause the common cold which was not seen in adults 3 . The study showed that antibody titers against all four proteins namely viral spike protein; the spike receptor-binding domain (RBD), the spike N-terminal domain (NTD), and the nucleocapsid (N) protein were greater among the children. Especially, the antibody titers against NTD and RBD were higher by 2.3-fold and 1.7-fold respectively.4
Further, studies revealed that the cellular immune response to the viral spike protein was stronger and greater than twice among than in adults 4. The S-protein is integrated over the surface of the virus; it leads to the attachment of the virus to the host cell surface receptors specifically angiotensin-converting enzyme 2 (ACE2) receptors which are found on the surface of many human cells, including those in the lungs allowing virus entry 3. The study revealed that the magnitude of the T-cell responses against the spike protein was 2.1 fold higher among seropositive children and more than half of the seronegative children, proposing pre-existing cross-reactive responses or sensitization to SARS-CoV-2.4
It was also observed that the children retained and had more antibodies and cellular responses even after 6 months following the infection, while it was reducing among adults. About 84% of children had cellular immune responses even after 6 months post-infection. Also, spike-specific response magnitude was greater in children than in adults.4
Thus, the above studies give evidence that children have a better memory in the immune cells, recognizes the pathogen quickly if encountered again, providing protecting against disease and reducing the complexities related to COVID-19.
- Subramanian Boopathi, A. B. P.,and Ponmalai Kolandaivelc. Novel 2019 coronavirus structure, mechanism of action, antiviral drug promises and rule out against its treatment. J Biomol Struct Dyn. 2020 1–10.