Written By: Longjam Dineshwori | Updated : January 7, 2021 6:08 PM IST
COVID-19 vaccine development relies on immune memory.
Can a person who have recovered from COVID-19 reinjected with the disease? How long an initial infection with SARS-CoV-2 provide immunity against the virus? These questions always spark a debate among researchers and medical professionals.
A new US study has suggested that durable immunity against secondary COVID-19 disease is a possibility in most individuals. In fact, the researchers found that patients who had recovered from COVID-19 have immune memory to the virus - in at least three immunological compartments - for up to 8 months after symptoms appeared.
"Immune memory, from either primary infection or immunization, is the source of protective immunity from a subsequent infection. Thus, COVID-19 vaccine development relies on immunological memory," the authors said. The research article was published in Science, a journal of the American Association for the Advancement of Science.
To understand immune memory to SARS-CoV-2, Jennifer Dan from the Center for Infectious Disease and Vaccine Research, La Jolla Institute for Immunology (LJI) and colleagues studied antibody and immune cell responses in more than 188 individuals (80 male, 108 female) from the United States who had recovered from COVID-19. Subject ages ranged from 19 to 81 years old.
The majority of subjects had a "mild" case of COVID-19, not requiring hospitalization. Only 7% of subjects were hospitalized, some of whom required intensive care unit (ICU) care.
Total 254 samples collected from the subjects were analysed. Most subjects provided a blood sample at a single time point, between 6 days and 240 days post-symptom onset (PSO), with 43 samples at 178 days or longer. Additionally, 51 subjects provided longitudinal blood samples over a duration of several months (2-4 time points), which allowed longitudinal assessment of immune memory. Their immune responses to SARS-CoV-2 were assessed over an interval of up to eight months post-infection by evaluating various components, including B cells (which produce more antibodies), and two types of T cells (CD8+ T cells and CD4+ T cells), which kill cells that are infected. They observed that each component of SARS-CoV-2 immune memory exhibited distinct kinetics.
Overall, the researchers said the antibodies only exhibited modest declines at six to eight months after symptom onset.
The authors, however, caution that "direct conclusions about protective immunity cannot be made on the basis of quantifying SARS-CoV-2 circulating antibodies, memory B cells, CD8+ T cells, and CD4+ T cells, because mechanisms of protective immunity against SARS-CoV-2 or COVID-19 are not defined in humans."
According to them, beyond sterilizing immunity, immune responses that confine SARS-CoV-2 to the upper respiratory tract (URT) and oral cavity would minimize COVID-19 disease severity to that of a 'common cold' or asymptomatic disease.
