Immunity and COVID

On 11 March 2020 WHO declared COVID-19 as a pandemic.¹ Coronavirus disease 2019 (COVID-19), caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), became a severe viral outbreak throughout the world affecting all spheres and categories of people making it a global concern. Among the many upcoming treatment methods enhancing, maintaining and lasting of the individual immunity plays a significant role.

Immunological protection plays an important role in body’s defense mechanism against any invasion in the body whether it is bacteria, virus, fungi, etc. The case of viral infections antiviral response is mediated through the T cells (thymus cells) and B cells (bone marrow-or bursa-derived cells). T cells are involved in cell-mediated immunity, whereas B cells are primarily responsible for humoral immunity (relating to antibodies). 

Immunological memory is a distinct aspect of the immune system.

To understand the immunological memory SARS-CoV-2, researchers’ Drs. Daniela Weiskopf, Alessandro Sette, and Shane Crotty from the La Jolla Institute for Immunology performed the studies discussed here. They measured the antigen-specific antibodies, memory B cells, CD4+ T cells, and CD8+ T cells in the blood from patients who recovered from COVID-19, up to 8 months after infection. The study included 254 samples from 188 COVID-19 patients, including 43 samples at 6 to 8 months after infection. 51 subjects in the study provided longitudinal blood samples, allowing for both cross-sectional and longitudinal analyses of SARS-CoV-2–specific immune memory. Antibodies against SARS-CoV-2 spike and receptor binding domain (RBD) declined moderately over 8 months, comparable to several other reports. Memory B cells against SARS-CoV-2 spike actually increased between 1 month and 8 months after infection. Memory CD8+ T cells and memory CD4+ T cells declined with an initial half-life of 3 to 5 months. This was the largest antigen-specific study to date of the four major types of immune memory for any viral infection which conclude that significant immune memory was generated after COVID-19, involving all four major types of immune memory and 95% of the patients retained immune memory at ~6 months after infection ².

In a similar study by the same group of researchers, they immune cells and antibodies from almost 200 people who had been exposed to SARS-CoV-2 and recovered were analyzed and found that Virus-specific B cells and Levels of T cells also remained high after infection. Six months after symptom onset, 92% of participants had CD4+ T cells that recognized the virus. About half the participants had CD8+ T cells, which kill cells that are infected by the virus. It was additionally observed that 95% of the participants had at least 3 out of 5 immune-system components that could recognize SARS-CoV-2 up to 8 months after infection ³.

In yet another study by Turner et al it was evident that people who have had COVID-19, that long-lived, memory plasma cells that produce antibodies are generated in the bone marrow. These cells provide long-term antibody production that offers stable protection at a level of 10–20% of that during the acute phase. Also Wang et al. studied and have characterized antibody responses at between six months and a year in SARS-CoV-2 patients; from which it is evident that the generation of immunological memory occurs and thus conclude that immunity can be boosted even further by vaccinating them after a year ⁴.

References: 

1. https://www.who.int/news/item/27-04-2020-who-timeline---covid-19
2. Jennifer M. Dan, J. M., Yu Kato, Kathryn M. Hastie, Esther Dawen Yu , Caterina E. Falit, Alba Grifoni ,Sydney I. Ramirez, Sonya Haupt , April Frazier , Catherine Nakao , Vamseedhar Rayaprolu ,Stephen A. Rawlings , Bjoern Peters, Florian Krammer, Viviana Simon , Erica Ollmann Saphire ,Davey M. Smith , Daniela Weiskopf , Alessandro Sette, Shane Crotty. Immunological memory to SARS-CoV-2 assessed for up to 8 months after infection. Science.,2021, 371.
3. https://www.nih.gov/news-events/nih-research-matters/lasting-immunity-found-after-recovery-covid-19
4. https://www.nature.com/articles/d41586-021-01557-z