Even before the pandemic, epidemiological evidence suggested that children in more developed countries, where handwashing and the use of sanitizer are more prevalent, might have less-developed immune systems compared to kids in developing nations who are routinely exposed to more bacteria, viruses and allergens.  
Ngakhale nthawi imene mliri unali usanabwere, sayansi yoona za kufala ndi kupewa matenda, inachitira umboni kuti ana a m'mayiko otukuka, komwe amasamba mmanja komanso kugwiritsa ntchito mankhwala ophera tizilombo toyambitsa matenda pafupipafupi, atha kukhala ndi chitetezo chofooka mnthupi kusiyana ndi ana a m'mayiko omwe akutukuka kumene omwe amakhala poyera ndi tizilombo toyambitsa matenda komanso kudwala kamba kodana ndi zinthu.