Study shows long-lived immunity after COVID-19

Protective immunity against COVID-19 has been shown to be robust in a recent study.

As the number of new hospital admissions for people with COVID-19 continues to decline (1), many sites are starting to relax restrictions and get life back to normal. Immunity to COVID-19 has increased due to vaccinations and natural immunity after infection. However, the question remains how long either immunity lasts (2).

In healthy adults, immunity is achieved regardless of the occurrence of infection – through vaccination or through natural disease (3). Doctors classify immunity as either acquired or natural. Vaccination and antibody transfer lead to acquired immunity, while infection / recovery and genetic transfer, for example through breast milk, lead to natural immunity (4).

Depending on the type and severity of the infection, immunity can be strong or weak (4). At the start of the COVID-19 pandemic, research suggested that natural immunity to COVID-19 lasted only two to three months (5). This raised concern that the natural immunity of patients with mild COVID-19 could be re-infected later.

To determine whether mild COVID-19 infection elicits long-lasting immunity, researchers at the Washington University School of Medicine in St. Louis conducted a study of the immune responses of 77 patients with mild COVID-19 and 11 people with no history of COVID – 19 (6).

During an infection, the body attacks antigens in a number of ways. The body's immune response first sends immune cells to surround and kill antigens, regardless of the type of infection.

Then the body's adaptive immune response creates B cells, which produce high levels of antibodies specifically designed to fight this antigen, and T cells to attack infected cells. B cells also produce plasma cells that make antibodies.

Some of these B and T cells become memory cells that recognize this antigen (7). Long-lived plasma cells also remain in the body's bone marrow and secrete small amounts of the antibody to protect against future infections (6).

There are different types of antibodies that perform different functions. One is immunoglobulin G (IgG), which coats microbes and speeds up their absorption by the immune system (4). Another is immunoglobulin A (IgA), which is concentrated in the mucous membranes and protects the body from infection (4).

In the study, blood samples were taken one, four, seven and eleven months after the onset of COVID-19 symptoms. Bone marrow samples were also taken from eighteen of the patients seven to eight and eleven months after infection.

The blood samples were analyzed for the presence of COVID-19 IgG, IgA and bone marrow plasma cells (BMPC). In the samples taken in the first few months after infection, the IgG and IgA levels were expected to be high. In the later samples, antibody levels fell and declined in most of the patients.

79 percent of BMPC samples contained antibody-producing cells, and memory B-cell levels were the same as those found in flu patients. The study suggested that the immune response to COVID-19 infection follows the normal natural immunity pattern (6).

The study had some limitations, however. The researchers were unable to detect any BMPCs in four samples, suggesting that levels in these cells may be below the detection limit. In addition, most of the patients studied had mild cases of COVID-19. It is not known if the response would be different for more severe COVID-19 infections.

Regarding severe infections, first author Dr. Jackson Turner in a press release: “It could go either way. Inflammation plays an important role in severe COVID-19, and too much inflammation can lead to faulty immune responses. On the other hand, often the reason people get really sick is because they have a lot of virus in their body and a lot of virus nearby can lead to a good immune response. So it's not clear. We need to repeat the study in people with moderate to severe infections to understand whether they are likely to be protected from re-infection. "

References

CDC. COVID data tracker. Centers for Disease Control and Prevention. Published March 28, 2020. Accessed May 26, 2021. https://covid.cdc.gov/covid-data-tracker/#new-hospital-admissions
Goldberg C, Pollak A. Bloomberg – Are You a Robot? www.bloomberg.com. Published on May 24, 2021. https://www.bloomberg.com/news/newsletters/2021-05-24/what-does-covid-immunity-look-like
Dinerstein C. Is Natural Immunity or Vaccination Better? American Council on Science and Health. Published March 19, 2021. Accessed May 26, 2021. https://www.acsh.org/news/2021/03/19/natural-immunity-or-vaccination-better-15409
US Department of Health and Human Services, National Institutes of Health, National Institute of Allergies and Infectious Diseases, National Cancer Institute. Understand the immune system how it works. NIH; 2003. Accessed May 26, 2021. http://www.imgt.org/IMGTeducation/Tutorials/ImmuneSystem/UK/the_immune_system.pdf
Long Q-X, Tang X-J, Shi Q-L, et al. Clinical and immunological evaluation of asymptomatic SARS-CoV-2 infections. Natural medicine. 2020; 26. doi: 10.1038 / s41591-020-0965-6
Turner J.S., Kim W., Kalaidina E. et al. SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans. Nature. Published online May 24, 2021. doi: 10.1038 / s41586-021-03647-4
Bucher K. The immune response. Accessed May 26, 2021 https://cdn.jamanetwork.com/ama/content_public/journal/jama/933829/jpg150012fa.png?Expires=1625020944&Signature=UbxiAQKTEPEWiPzg3EkfPoZFHGriCBCcQ1ws9VnY0E1D1cehI493KsHKmb3r6vL51r80yyNuGbvxrD91nmMtIou1Ybzwvv~Xlr0CvE-~oygqheGGU~o6wayTIISHrY~rk8M-OoxSuOEAy2px0oC93Z2KfJtEcU1Jeh16XCYQ4k8GPUIMFkmIN3kwydjNjjbaIATTrnUXgxniCCwlN3XAeDAwCfFPl9KgjrYgHyQvj8-M28jv8a6TaBQOk0ZSJgJYfVpFvrbwd1xn-- 7QUq8Ywbo4OlV2KJ2jeNERUZwQ8Norw1 -rYOac-lLml4aUOICInU5-SuLW3wI2gjtzNn6Rdw __ & Key-Pair-Id = APKAIE5G5CRDK6RD3PGA
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