Part II: What About the Long Run, Is there Lasting Immunity?
Once the immune system is successful at fighting off a threat like the SARS CoV2 virus it can begin to relax. Because the antigen is no longer around after a person finally recovers, there’s no need to continue to mount the immune response. The immune system keeps some antibodies around for a while just in case the person is exposed to the virus again. If that does happen, then the antibodies (IgG), are at the ready and can neutralize the virus right away and draw in a few phagocytes to kill the virus before it replicates.
After a couple of years have passed and the body hasn’t seen the virus around, it often begins to stop making those antibodies. But it has a memory. Even if all the antibodies are gone from the blood, the immune system will remember that virus- even decades later in some cases.
The B Cells that make the antibodies stand at the ready to make new antibodies right away and they won’t have the learning curve like they had the first time. Likewise, the T cells that specialized in attaching the virus will be at the ready. Even when those original B and T cells eventually die- their offspring still remember the old virus and can ramp up fast.
Will People that Recover have Lasting Immunity? All indications are yes. An article recently published in the highly respected journal Nature found that patients who had recovered from COVID-19 mounted a full immune response that included the production of antibodies (via B cells), complement fixing, while blood cell production (phagocytes) and a robust T cell response.
This is an important finding that informs whether people that have recovered from a COVID-19 infection are protected from additional infections. The data in this study strongly suggest that the answer to that question is “yes, there is lasting immunity”.
Indeed, even after antibody production (titer) wanes after a period of months or years, the evidence suggests that memory B cells will be around to produce antibodies quickly if needed. In addition, the study shows that specific T cells with memory will also be around to mount a specific response to a future exposure to the virus.
A separate study published in the British Medical Journal found that “recovered individuals developed SARS-CoV-2-specific IgG antibody and neutralizing plasma, as well as virus-specific memory B and T cells that not only persisted, but in some cases increased numerically over three months following symptom onset. These findings demonstrate that mild COVID-19 elicits memory lymphocytes that persist and display functional hallmarks associated with antiviral protective immunity.”
