The clinical features and immune responses of asymptomatic individuals infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have not been well described. We studied 37 asymptomatic individuals in the Wanzhou District who were diagnosed with RT–PCR-confirmed SARS-CoV-2 infections but without any relevant clinical symptoms in the preceding 14 d and during hospitalization. Asymptomatic individuals were admitted to the government-designated Wanzhou People’s Hospital for centralized isolation in accordance with policy1. The median duration of viral shedding in the asymptomatic group was 19 d (interquartile range (IQR), 15–26 d). The asymptomatic group had a significantly longer duration of viral shedding than the symptomatic group (log-rank P = 0.028). The virus-specific IgG levels in the asymptomatic group (median S/CO, 3.4; IQR, 1.6–10.7) were significantly lower (P = 0.005) relative to the symptomatic group (median S/CO, 20.5; IQR, 5.8–38.2) in the acute phase. Of asymptomatic individuals, 93.3% (28/30) and 81.1% (30/37) had reduction in IgG and neutralizing antibody levels, respectively, during the early convalescent phase, as compared to 96.8% (30/31) and 62.2% (23/37) of symptomatic patients. Forty percent of asymptomatic individuals became seronegative and 12.9% of the symptomatic group became negative for IgG in the early convalescent phase. In addition, asymptomatic individuals exhibited lower levels of 18 pro- and anti-inflammatory cytokines. These data suggest that asymptomatic individuals had a weaker immune response to SARS-CoV-2 infection. The reduction in IgG and neutralizing antibody levels in the early convalescent phase might have implications for immunity strategy and serological surveys.
Does immunity last beyond antibodies?
Usually not by my understanding. If your B cells have forgotten about the antigen, it will stop producing antibodies. But I’m not an expert, so I looked this up and found this:
TA: Not all antibodies last forever. Why does immunologic memory sometimes fade?
Fogle: We still don’t know how, why and for how long immunologic memory lasts for every infectious disease. Immunologic memory is probably one of the most complicated things we study in immunology. What we do know for most pathogens and vaccines is that, especially from childhood to adolescence, if we are exposed to something multiple times, we generate robust and long-term immunity.
But as we age, although we may develop some adaptive immunity, the memory doesn’t seem to last as long. This probably has to do with the age at which we’re exposed to the pathogen and how good the pathogen is at inducing immunity. It is also linked to how many times we are exposed to or vaccinated against a pathogen. We generally generate our maximal number of memory cells with three to five exposures, meaning that being exposed more than three to five times will not further increase the overall number of memory cells.
Taken from the Q and A on COVID-19: medicalxpress.com/news/2020-05-dont-antibodies-immunity.html