FCGR2A and COVID-19: Notably, a recent longitudinal study of primary healthcare workers in the CovidCatCentral cohort (Barcelona, Spain) reported that higher post-vaccination ratios of IgG4 + IgG2 over IgG1 + IgG3 correlated with increased risk of symptomatic COVID-19, whereas neutralization activity and FcγR binding were associated with a reduced infection risk52.