Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system of unknown etiology. We tested the hypothesis that MS is caused by Epstein-Barr virus (EBV) in a cohort comprising more than 10 million young adults on active duty in the US military, 955 of whom were diagnosed with MS during their period of service. Risk of MS increased 32-fold after infection with EBV but was not increased after infection with other viruses, including the similarly transmitted cytomegalovirus. Serum levels of neurofilament light chain, a biomarker of neuroaxonal degeneration, increased only after EBV seroconversion. These findings cannot be explained by any known risk factor for MS and suggest EBV as the leading cause of MS.

Test sensitivity is secondary to frequency and turnaround time for COVID-19 screening.

It’s time to change how we think about the sensitivity of testing for Covid-19. The Food and Drug Administration (FDA) and the scientific community are currently almost exclusively focused on test sensitivity, a measure of how well an individual assay can detect viral protein or RNA molecules. Critically, this measure neglects the context of how the test is being used. Yet when it comes to the broad screening the United States so desperately needs, context is fundamental. The key question is not how well molecules can be detected in a single sample but how effectively infections can be detected in a population by the repeated use of a given test as part of an overall testing strategy — the sensitivity of the testing regimen.

The toll of measles on the immune system: Many of the deaths attributable to measles virus are caused by secondary infections because the virus infects and functionally impairs immune cells. Whether measles infection causes long-term damage to immune memory has been unclear. This question has become increasingly important given the resurgence in measles epidemics worldwide. Using a blood test called VirScan, Mina et al. comprehensively analyzed the antibody repertoire in children before and after natural infection with measles virus as well as in children before and after measles vaccination. They found that measles infection can greatly diminish previously acquired immune memory, potentially leaving individuals at risk for infection by other pathogens. These adverse effects on the immune system were not seen in vaccinated children. Science , this issue p. 599

Extra dividends from measles vaccine: Vaccination against measles has many benefits, not only lifelong protection against this potentially serious virus. Mina et al. analyzed data collected since mass vaccination began in high-income countries when measles was common. Measles vaccination is associated with less mortality from other childhood infections. Measles is known to cause transient immunosuppression, but close inspection of the mortality data suggests that it disables immune memory for 2 to 3 years. Vaccination thus does more than safeguard children against measles; it also stops other infections taking advantage of measles-induced immune damage. Science , this issue p. 694

Michael R Tom, Michael J Mina; To Interpret the SARS-CoV-2 Test, Consider the Cycle Threshold Value, Clinical Infectious Diseases, , ciaa619, https://doi.org/1