Study on the human immune response to COVID-19.

Key Facts:-

• When infected by a virus, non-specific immune responses in the form of macrophages, neutrophils, and other cells tend to prevent the virus from causing symptoms.
• Soon after, the body makes antibodies specific to the virus called the immunoglobulins — IgG and IgM, called the adaptive response.
• In addition, cellular immunity kicks in when the body makes T cells that destroy cells that have been infected by the virus.
• The combination of adaptive response and cellular immunity may help prevent progression to severe illness or re-infection by the same virus. This process is often measured by the presence of antibodies in the blood.

Details:

• A study published in Nature Medicine suggests that antibodies formed against SARS-CoV-2 begin to decrease in number, just two-three months after infection.
• The study observed that IgG levels and neutralizing antibodies in a high proportion of individuals who recovered from SARS-CoV-2 infection start to decrease within two-three months after infection. This is unlike for 2002-2003 SARS and MERS coronavirus in which case the antibodies were found to last for longer periods.
• This does not necessarily mean that people previously infected with SARS-CoV-2 can be reinfected soon after. The study notes that even if the antibody level decreases, it might still be protective.
• Besides inducing neutralizing antibodies, novel coronavirus has also been found to induce cellular immunity. As a result, the immune system’s T cells and B cells are elevated in an infected person.
• B cells produce antibodies.

Implications:

• The reduction in IgG and neutralizing antibody levels in the early convalescent phase might have implications for the immunity strategy and serological surveys being undertaken.
• These data might indicate the risks of using COVID-19 ‘immunity passports’ and support the prolongation of public health interventions, including social distancing, hygiene, isolation of high-risk groups, and widespread testing.