Dr Simon Clarke, Associate Professor of Cellular Microbiology at the University of Reading, said:
“The authors of this study show that people with higher amounts of antibodies reactive to the mumps virus, had less severe Covid-19 symptoms. Unfortunately, the authors appear not to have determined the total concentration of antibodies in the blood of these patients, so it might be the case that they just had higher concentrations of all antibodies in their blood, not just those which are reactive to mumps. This merely demonstrates a correlation, which as always is not evidence of causation. There is no confirmation that it is the anti-mumps antibodies that is causing the decrease in severity of symptoms.”
The authors looked at concentrations of antibodies to mumps, measles, and rubella. They found no link between covid severity and levels of measles or rubella antibodies but did find a link between severity and mumps antibodies. So is this criticism really valid?
From this abstract: https://mbio.asm.org/content/11/6/e02628-20
Our aim was to determine whether any MMR IgG titers are inversely correlated with severity in recovered COVID-19 patients previously vaccinated with MMR II.
There was a significant inverse correlation (rs = −0.71, P < 0.001) between mumps virus titers (mumps titers) and COVID-19 severity within the MMR II group. There were no significant correlations between mumps titers and severity in the comparison group, between mumps titers and age in the MMR II group, or between severity and measles or rubella titers in either group.
MMR IgG titers were measured in 80 adults who had consented to join our study.
Mumps, measles, and rubella IgG titers were measured by Quest Diagnostics using Liaison analyzers with chemiluminescence immunoassay (CLIA) technology for the qualitative determination of IgG antibodies in human serum specimens. The method for qualitative determination of each specific IgG corresponding to each virus was an indirect CLIA.
The significant inverse correlations that we observed in the MMR II group between mumps titers and severity, as well as between mumps titers and symptom scores, indicate that there is an association between mumps titers and COVID-19. This significant inverse correlation existed at all ages. In contrast, similar associations were not identified for measles or rubella titers.