Identifying individuals within these groups from health records may be challenging and could lead to some individuals not being identified for vaccination (the underserved population).
Gall nodi unigolion yn y grwpiau hyn o gofnodion iechyd fod yn heriol a gallai arwain at beidio â nodi rhai unigolion ar gyfer y brechlyn (y boblogaeth na wasanaethir yn ddigonol).