@skematica Definitely coincidence. Ever considered you might be infecting them?
But seriously, immune boosting is bunk. https://www.sciencebasedmedicine.org/boost-your-immune-system/ and http://www.slate.com/articles/healthandscience/medicalexaminer/2014/12/boostyourimmunitycoldandflutreatmentssuppressinnateimmune_system.html
// @JeremyCherfas