> First, we observed three types of antibody responses in COVID-19 patients, strong, weak and non-response. Second, we found that the earlier response, higher antibody titer and higher proportion of strong responders for IgM and IgG were significantly associated with disease severity. Third, the weak responders for IgG antibodies had a significantly higher viral clearance rate than that of strong responders. These data indicates strong antibody response is associated with disease severity, and weak antibody response is associated with viral clearance, which resembles SARS and MERS.

I have a wild-ass guess. I vaguely recall that antibody response and cellular immune response generally tend to be inversely proportional. And that IgM antibody response is an aspect of allergy. So maybe strong antibody responders tend to have weaker cellular responses, and more wet lung problems.