A review of 33 published and unpublished reports has found that people vaccinated against measles occasionally passed the virus to someone else, a result the authors say should change how health departments investigate outbreaks rather than how families think about the vaccine.
The review and meta-analysis, led by researchers at Public Health Ontario and published in Expert Review of Vaccines, examined records covering 890 vaccinated people with confirmed measles. Of those, 70 (7.9%) transmitted the virus to at least one other person. Those transmissions produced 237 direct secondary cases, a median of two per transmitter. The authors also traced 812 measles cases in total back to a vaccinated source, with a median outbreak size of four cases.
