The news media can influence how the public and policymakers feel about vaccination. Perhaps under the impression that such messages can be fear-inducing and thus mobilizing, the media often laments low immunization rates. This could, however, activate a powerful descriptive social norm (“many people are not getting vaccinated”) and may be especially ill-advised in the absence of a herd-immunity explanation (that if enough people have immunity through vaccination, the virus is contained). To identify typical media practices, we analyzed the content of 160 vaccination-related news stories by nine highest-trafficked news websites in Serbia, published July–December 2017, around the start of the measles outbreak. We coded both the news story as a whole and every vaccination-rate mention (N = 339). News stories framed current vaccination rates and changes in vaccination rates in a predominantly negative way (175/241 and 67/98, respectively) (e.g., “only 50% vaccinated”, “fewer parents vaccinating their children”). A total of 24/86 of news stories mentioning vaccination rates did not provide any numerical values. Reference groups for vaccination rates were rarely specified. Out of the 32 news stories mentioning the term herd or collective immunity, 11 explained the effect. We show that even routine communication of vaccination rates can be biased through (often negatively valenced) attribute frames and imprecise descriptions. We provide initial recommendations for news media organizations and journalists, including strategies to promote positive dynamic norms and prescriptive norms and explain benefits of herd immunity.