Maybe I'm misreading the article (or your post), but isn't that first article saying exactly the opposite? > When someone is infected with a virus they’ve seen

Maybe I'm misreading the article (or your post), but isn't that first article saying exactly the opposite? > When someone is infected with a virus they’ve seen before, the immune system tends to pump out antibodies created during the first infection. That immune memory normally helps fight off secondary infections faster, but that memory can occasionally backfire if the virus has mutated in the right way to evade those original antibodies – as happened with last year’s flu. i.e. youth exposure to a particular 70s/80s strain of the flu virus actually worsened the immune response in 2014?