COVID-19 Antibodies and Immunity

Author: Alison MacPhee

With the number of resolved cases in Canada increasing and the number of active cases on a steady decline, a new question arises: are those who have been previously infected by COVID-19 immune to future infections? Many researchers around the world have been trying to answer this very question using antibody tests on people who have recovered from the virus [2]. Additionally, they have been studying comparisons with past epidemics and pandemics.

Our immune system is often referred to as the body’s natural defense mechanism. On a cellular level, it is made up of white blood cells, or more specifically, B and T lymphocytes [1,6]. When an antigen, a foreign substance carried by viruses, enters the body, the B cells are responsible for recognizing it [1,6]. They create a highly important part of the immune response: antibodies. Antibodies are Y-shaped proteins that help eliminate virus particles by either blocking them from healthy cells or destroying them altogether [1,2,6]. Each type of antibody is specific to one antigen (imagine a key that only fits one lock) [1,2,6]. After the antibodies mark the antigen, the T cells are sent to destroy it [1, 6]. When a person recovers from a virus, a small number of antibodies remain in the body so that if reinfection does occur, the immune response will be much quicker [2].

The disease we know as COVID-19 is caused by the SARS-CoV-2 strain [3]. These particles have proteins on their surface that resemble spikes, which allow them to latch onto healthy human cells and reproduce [3,8]. A successful vaccine would trigger the production of antibodies that would attack these “spikes” and prevent the reproduction of the virus since a virus is useless without a host [3]. However, to develop a vaccine like this, scientists have been studying antibodies that already exist: those produced in a person after a previous COVID-19 infection. It is important to determine how many antibodies are left after infection, as well as how long they remain in the body [3]. 

Dr. Davide Robbiani and Dr. Michel Nussenzweig at Rockefeller University conducted a study in June 2020 on 149 people who had previously contracted and recovered from COVID-19 [3]. Unfortunately, the majority of participants had low or very low levels of antibodies, and only 1% of participants had a sufficient amount to neutralize the virus [3]. Although that sounds discouraging, this study proved to be beneficial too. All antibodies that were observed were able to be grouped into three distinct categories based on similarities, which contributed greatly to help scientists designing vaccines [3]. If a vaccine elicits one of these types of antibodies, the developer knows they are making progress [3]. Other studies explain more specifically that most patients lose their antibodies within 2-3 months [4,5]. This is very different from previous SARS and MERS epidemics, where antibodies lasted for almost a year [4]. It has also been observed that asymptomatic patients were more likely to have low or very low antibody levels compared to those who exhibited more severe symptoms [4, 5]. Overall, more research is still needed to further understand these topics, as they are very recent developments. 

As it stands, the majority of the human population is still vulnerable to COVID-19 and will be until herd immunity is established [6]. Herd immunity exists when a certain proportion of a population is immune to a given sickness [6,7]. This threshold is different for every disease, depending on how contagious it is [7]. Currently, the threshold population for the novel coronavirus is uncertain, but experts estimate at least 70% of the population would have to be immune, either from infection or vaccination, to halt community transmission [7]. However, a vaccination would be ideal to limit serious health complications that could result from the virus [6, 7].

Until a vaccine is developed, it is crucial to follow proper health and safety precautions, including physical distancing, wearing masks in public, frequent hand washing, and staying home if sick [7].

Editors

Jasmine Kokkat, and Rhea Verma

Designers

Richard Chen

Additional Credits

Header Image by Camilo Jimenez @coolmilo from Unsplash

SARS-CoV-2 Particle Image from Sunday Assembly Atlanta

References