'Something's wrong with the data. There are too few people in hospitals' with respiratory syncytial virus (RSV), epidemiologist Caroline Klint Johannesen recalls a colleague remarking while analysing Danish health records for last winter. On 1 October 2025, Denmark introduced a nationwide policy of vaccinating pregnant people against RSV ' a respiratory pathogen that usually causes mild symptoms but can lead to severe disease and even death in vulnerable people, including infants and older adults. Maternal antibodies induced by the vaccine cross the placenta to protect babies for around the first six months of their lives, when they are most at risk. Newborns at high risk of severe disease, including premature infants, whose mothers had not been vaccinated, were given injections of monoclonal antibodies. The World Health Organization (WHO) estimates that every year, RSV hospitalizes roughly 3.6 million and kills about 100,000 children under 5 years old. Of these deaths, 97% occur in...
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