Unsupervised principal-component analysis (PCA) of 129 seroreactive antigens for adults and children from different geographical locations. Unsupervised principal-component analysis (PCA) of 129 seroreactive antigens for adults and children from different geographical locations. (A) Children (0 to 5 years old); (B) adults (>20 years old). Samples are color coded in accordance with the geographical location, as indicated on the plot. Tamaki Kobayashi et al. mSphere 2019; doi:10.1128/mSphereDirect.00061-19