HMM: Coronavirus: low antibody levels raise questions about reinfection risk. “Researchers in Shanghai hope to determine whether some recovered coronavirus patients have a higher risk of reinfection after finding surprisingly low levels of Covid-19 antibodies in a number of people discharged from hospital. A team from Fudan University analysed blood samples from 175 patients discharged from the Shanghai Public Health Clinical Centre and found that nearly a third had unexpectedly low levels of antibodies. In some cases, antibodies could not be detected at all.”

UPDATE: So some possibilities: The report could be false, or mistaken. Either is possible, and doubly so coming out of China. Or these people never had Covid-19 at all. Alternatively, it’s the innate immune system rather than the adaptive immune system that is key. Kids generally get few symptoms and their innate immune systems are much stronger than adults’. Maybe an effective innate immune response doesn’t produce a strong antibody count because it kills the disease off first.