The pandemic has subsided; the number of people who have recovered from COVID19 (SARS-CoV-2) have been steadily rising. With this new development, the question of how long the immunity against the virus will last remains a cause for concern for experts, including the general public.
A new study has found that the immunity against COVID-19 post recovery remains for at least six months and likely even longer.
In the paper published in the journal Nature, the researchers note that the immune system studies the nature of the virus remarkably well and strategize itself to develop better and more effective antibodies even after the infection has abated.
Now before we get further into detail, let’s first understand how our immune system protects us from many different types of unwanted invaders, including viruses, bacteria, parasites, and fungi, and how it helps us attain immunity against them.
The immune system is an army of cells, tissues, and organs that coordinate the bodily defenses against any threats. The white blood cells, also known as leukocytes, are one of the most important cells involved in the process, and they circulate throughout the body and make sure there are not any unwanted foreign invaders that may harm us.
There are two divisions of leukocytes, and they are: phagocytes and lymphocytes.
Phagocytes are the first cells to trigger immune response; they destroy any foreign cells they encounter through ingestion. This helps them identify the antigen present in the foreign cells, and transmit this information to lymphocytes, which then hunt for infected body cells and annihilate them completely.
The lymphocytes unit of the immune system comprises of two major cellular components called B-cells and T-cells. These cells utilize the information collected from the antigens to recognize any unwanted visitors in the future. So once a threat makes another visit, the cells will unleash the right antibodies to destroy the invaders. This is how our body develops immunity against certain diseases.
However, the effectiveness of immune response decreases with time as the level of antibodies drops after a certain period. So in order to deal with pathogens more efficiently, the immune system doesn’t always produce antibodies, instead it resorts to creating memory B-cells that easily recognize the pathogen and release a new batch of antibodies upon re-exposure to the any unwanted visitors.
In the study, the researchers found that these antibodies emerged post SARS-CoV-2 infection are the results of immune cells working in choir to evolve while simultaneously being constantly exposed to hidden remnants of the virus in the intestinal wall. And as a result, the next time a recovered patient contracts the virus, their body will initiate a rapid immune response to the virus, hence preventing reinfection. However, the efficacy of this memory on warding off the infection is solely determined by the nature of the pathogen the person has contracted with.
For the study, the researchers assessed the antibody responses of 87 participants at two separate time-points: one month following infection, and then again after six months. They found that although the antibodies lingered on the participants’ blood plasma for six months, there were significant drops in their levels and as a result of that, the ability to neutralize the virus plummeted five-fold.
Surprisingly however, the subsequent batch of antibodies produced by the memory B cells in patients, increased in some cases. The researches have specified that the overall numbers of memory B-cells that unleashed antibodies that attack the receptor-binding domain of the virus, remained the same. These antibodies are the ones that will fend off the virus upon re-encounter.
Also, upon closer inspection at the memory B cells, the team also found that these cells had mutated many times over even after the infection waned, and this made the antibodies the cells created outperformed the originals in staving off the virus. Moreover, this new set of antibodies could latch on to the virus and even identify the mutated versions of it.
They have been found to be able to identify even the mutated version of SARS-CoV-2 including South African Variants (called 501Y.V2) that have undergone mutations for more than 20 times.
The memory B cells of course mutate and deploy antibodies at times of infections like HIV or herpes, but seeing them evolve with SARS-CoV-2, which is believed to wither soon after infection has resolved, was never expected until now.
SARS-Cov-2 thrives and replicates in the upper respiratory tract. However, upon examining biopsies of intestinal tissue from recovered patients, its genetic materials and proteins were detected within it. The researchers conjecture this could be what’s fueling the evolution of memory B-cells.
The infectiousness of these viral remnants are yet to be determined. In the future, the team plans to understand the role these viral remnants play in immunity as well as in the progression of the disease by making more participants involved.
The study has been published in the journal Nature:
Gaebler, C., Wang, Z., Lorenzi, J.C.C. et al. Evolution of antibody immunity to SARS-CoV-2. Nature (2021). https://doi.org/10.1038/s41586-021-03207-w