The study actually points out the the lactoferrin used in this in vitro study is specialized and NOT from milk.
I read the study paper, itself.
The lactoferrin was an 85+% extract from human female breast milk provided by Millipore Sigma.
Of note, lactoferrin from women is about 90% apolactoferrin and 10% normal lactoferrin.
Fortunately, apolactoferrin is the form more supplements recently use, which they state is just “Lactoferrin.” Case in point is Jarrow Formula’s “Lactoferrin.” It is 100% apolactoferrin, but is named “Lactoferrin.”
It is safe to interpret the “lactoferrin” from the study was about 10% normal lactoferrin (“hololactoferrin” with ferric iron) and 90+% apolactoferrin, which, when used in the study, would provide great insight into how babies across the world are surviving COVID-19 so easily.
Cows make the exact same lactoferrins, but in a different proportion.
The source is irrelevant. Lactoferrin is lactoferrin...that is just basic chemistry.