COVID-19 research needs interactive reliable biomarkers at genomic and genetic levels. Earlier research has established the existence of genomic signature patterns and nearly perfect reliable interactive genomic biomarkers. However, reliable DNA methylation markers haven't been identified at the epigenetic level, not to mention interactiveness. This study utilized the newly proven and powerful method to discover nearly perfect interactive COVID-19 DNA methylation markers. From 865,859 methylation sites, a miniature set of seven Infinium MethylationEPIC sites (CpG sites, genes) and one intergenic region have been discovered to interact with each other and with disease subtypes. They lead to nearly perfectly (96.87-100% accuracy) predicting COVID-19 patients from patients presenting with respiratory symptoms but not COVID-19. These seven CpG sites regulated genes differ from the optimum COVID-19 genomic biomarker genes reported in our earlier work. These CpG sites also lead to an accuracy of 92.88% with a sensitivity of 100% and a specificity of 91.30% in the study of pediatric COVID-19 cases and healthy controls. It is found that site-site interactions between adults and children are different. Further, they show strong performance in separating Multisystem Inflammatory Syndrome in Children (MIS-C) from pediatric COVID-19 cases with an accuracy of 94.83%, a sensitivity of 95.35%, and a specificity of 93.33%. In addition, these seven CpG sites reach high performance in separating COVID-19 severe and mild cases and normal cases. These seven CpG sites can jointly explain some post COVID-19 related diseases. These seven CpG sites and the optimum performed genomic biomarkers reported in our earlier work rise to be potential druggable targets. Among these seven CpG sites, diseases associated with cg16785077 (gene MX1) can have an incubation period of up to six to eight years, which raises a serious (or urgent) issue to investigate now or sooner.