https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917921/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917921/ https://link.springer.com/article/10.1007/s40629-01

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917921/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917921/ https://link.springer.com/article/10.1007/s40629-018-0056-0 https://link.springer.com/article/10.1007/s40629-018-0056-0 https://www.sciencedirect.com/topics/immunology-and-microbiology/heterologous-immunity https://www.sciencedirect.com/topics/immunology-and-microbio... If all the original author had done was ask for evidence for the claim, it would be completely fair that the burden of proof was entirely on the parent commenter to which they replied based on our social standards. However, they themselves made a specific claim that the parent commenter was wrong and did nothing to back it up. As such a burden of proof was on them as well at that point for the exact same reason.