I'm not familiar with the literature, but I did read the paper. They looked at military personnel who have had samples taken and saved, and were able to 'go ba

I'm not familiar with the literature, but I did read the paper. They looked at military personnel who have had samples taken and saved, and were able to 'go back in time' to look their EBV status at enrolment and later on. They found that either having previously had EBV or acquiring EBV after enrolment increased your risk of having MS. However, to put things in context, more than 90% of the population will be exposed to EBV, so I'm not 100% sure how to interpret this. It might be better to think of the headline as 'EBV seronegative people are protected from MS', given people who are 'seronegative' (their immune system doesn't show any evidence of them fighting the disease) are the minority population here. The paper talks about the possibility of a confounding factor and reverse-causation, though I think the focus is too much on the EBV seropositive population and it would be interesting to think about what is unusual about the EBV seronegatives.