When any virus enters the body, immune cells immediately churn out hordes of circulating antibodies. Foot soldiers of the immune system, these antibodies burn bright but decay at variable rates depending on the vaccine or infection—they may protect us for months or years but then dwindle in number, allowing possible reinfection.
The immune system has a backup plan: An elite cadre of memory B cells that outlive circulating antibodies to produce so-called memory antibodies that provide long-term protection. Studies suggest that memory B cells for smallpox last at least 60 years after vaccination; those for Spanish flu, nearly a century. And while memory B cells don't necessarily block reinfection, they can prevent severe disease.
Recent studies have suggested that within five months of receiving a vaccine or recovering from a natural infection, some of us no longer retain sufficient circulating antibodies to keep the novel coronavirus at bay, but our memory B cells stand vigilant. Until now, however, scientists did not know whether the vaccines could be expected to provide the sort of robust memory B cell response seen after natural infection.
https://medicalxpress.com/news/2021-08-differences-covid-antibody-responses-emerge.html
heere you go Hokusai.... this is an excellent explainer and well worth a read.
