Scientists solve a dengue mystery: Why second infection is worse than first (self.COVID19)
submitted 16 minutes ago * by mobo392
This may be informative as to why there are reports of a more severe reaction to 2019-nCoV re-infection:
Too much or too little—better than some Dengue fever is caused by a mosquito-transmitted flavivirus resembling Zika virus. Both viruses can cause severe diseases in humans with catastrophic sequelae. It has been suspected in humans, and shown in animal models, that the host's immune responses can make disease worse. Katzelnick et al. examined data from a long-term study of Nicaraguan children exposed to dengue virus (see the Perspective by Feinberg and Ahmed). They confirmed that antibody-dependent enhancement of disease occurs at a specific range of antibody concentrations. Low levels of antibody did not enhance disease, intermediate levels exacerbated disease, and high antibody titers protected against severe disease. These findings have major implications for vaccines against flaviviruses. Indeed, recent vaccine trials have shown evidence of severe disease in some recipients who were previously exposed to virus.
https://science.sciencemag.org/content/358/6365/929This sounds similar to what was reported in animal trials of SARS vaccines:
These SARS-CoV vaccines all induced antibody and protection against infection with SARS-CoV. However, challenge of mice given any of the vaccines led to occurrence of Th2-type immunopathology suggesting hypersensitivity to SARS-CoV components was induced. Caution in proceeding to application of a SARS-CoV vaccine in humans is indicated.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3335060/There was some laypress coverage here:
Harris and her colleagues found that when antibody levels fell to a certain point in children who had been previously infected, they were at greater risk of having severe dengue disease if they were again infected. In fact, for children whose antibodies fell to within this low range — a sort of anti-sweet spot — the risk was nearly eight times higher than for other children.
In contrast, higher antibody levels were protective against severe illness.
The belief is that low levels of antibodies cannot neutralize or kill the invading viruses. But they do bind to them and effectively usher them into susceptible cells, where the viruses then replicate.
Perhaps the adults having severe illness had previous exposure to other coronavirus strains like SARS, while children have not? SARS was 17 years ago at this point.