The phrase "new strain" refers to a new or different version of something, usually referring to a type or variation of a virus or disease that has slightly changed or evolved. Full definition
This is very important in order to be sure that your dog is completely better, but also to not create new strains of antibiotic resistant bacteria. (topdogtips.com)
A new discovery could help farmers develop new strains to feed the world even as carbon dioxide levels rise. (psmag.com)
But caring for babies and children can also put new strains on your relationship. (raisingchildren.net.au)