Omicron variant susceptibility to neutralizing antibodies induced in children by natural SARS-CoV-2 infection or COVID-19 vaccine

The novel SARS-CoV-2 Omicron variant may increase the risk of re-infection and vaccine breakthrough infections as it possesses key mutations in the spike protein that affect neutralizing antibody response. Most studies on neutralization susceptibility were conducted using specimens from adult COVID-19 patients or vaccine recipients. However, since the paediatric population has an antibody response to SARS-CoV-2 infection that is distinct from the adult population, it is critical to assess the neutralization susceptibility of pediatric serum specimens. This study compared the neutralization susceptibility of serum specimens collected from 49 individuals of <18 years old, including 34 adolescent BNT162b2 (Pfizer-BioNTech) vaccine recipients, and 15 recovered COVID-19 patients aged between 2 and 17. We demonstrated that only 38.2% of BNT162b2 vaccine recipients and 26.7% of recovered COVID-19 patients had their serum neutralization titre at or above the detection threshold in our live virus microneutralization assay. Furthermore, the neutralizing antibody titer against the Omicron variant was substantially lower than those against the ancestral virus or the Beta variant. Our results suggest that vaccine recipients and COVID-19 patients in the pediatric age group will likely be more susceptible to vaccine breakthrough infections or reinfections due to the Omicron variant than previous variants

Fertility study of complement-3 in mice

Session: SRB Orals - Embryo DevelopmentHuman oviductal cells produce complement-3 (C3) and its embryotrophic derivative, iC3b in the presence of embryos. We proposed that C3-deficiency would lead to fertility impairment in mice in vivo. To determine the physiological significance of this protein in reproduction, heterozygous mice carrying the mutated C3 gene (C57BL/6J-C3tmlCrr) were purchased from Jackson Laboratory. Crossing of these mice (C3+/-) generated mice carrying the homozygous (C3+/+) and mutated C3 (C3-/-) genes. C3-/- and the wild type C3+/+ were allowed to cage with males of the same genotype for 6 months and their fertility was examined. Both genotypes are fertile and produce viable pups. The number of litters per week born from C3-/- pairs (0.116±0.05) were significantly smaller than those in C3 +/+ pairs (0.168±0.04). There were no significant difference between the mean numbers of pups per litter, mean born weight and mean litter size at wean between the two groups. However, the mean pup weight at weaning of C3 -/- pairs (8.1± 1.2 g .) was significantly smaller than that of C3 +/+ pairs (8.6±1.3 g). Although C3 protein could not be detected in the C3 -/- mice serum by Western blot, C3 immunoreactivity and mRNA was detected in the oviduct and liver tissues homogenate, suggesting the presence of mutated C3 molecules in these animals. These mating results suggested that the C3 -/- mice require longer getting pregnant and the resulting pups are smaller in size at weaning. The biological activity of the mutated C3 molecule on embryo development remains to be investigated