Denmark’s nationwide vaccination policy for pregnant people, launched on October 1, 2025, has triggered a sharp decline in infant hospital admissions for respiratory syncytial virus (RSV).
The initiative relies on maternal antibodies crossing the placenta to shield newborns during their first six months of life.
“Something’s wrong with the data. There are too few people in hospitals,” Caroline Klint Johannesen, an epidemiologist at Nordsjællands Hospital in Hillerød, Denmark, recalls a colleague remarking.
Johannesen observed that infant hospitalizations plummeted after the rollout. For newborns at high risk of severe disease whose mothers had not been vaccinated, the country provided injections of monoclonal antibodies.
The virus is a global health burden. The World Health Organization estimates that RSV hospitalizes roughly 3.6 million children under 5 years old annually, resulting in about 100,000 deaths. According to the organization, 97% of these fatalities occur in low- and middle-income countries.
The pathogen also threatens older adults, particularly those over 60 with chronic heart or lung conditions. In the United States, the Centers for Disease Control and Prevention estimates that RSV-related deaths have ranged between 10,000 and 25,000 in each of the past two winters.
The medical toolkit to combat RSV has expanded since 2022, when European regulators approved nirsevimab, a long-acting monoclonal antibody. Since then, a second antibody and three vaccines have been developed for use in adults, one of which is suitable for pregnant people.
“It’s just remarkable,” said Buddy Creech, a paediatrician at Vanderbilt University in Nashville, Tennessee. “To have gone from no mechanism to prevent RSV to an embarrassment of riches.”
Dozens of countries across Europe, Asia, and North and South America have now launched immunization programmes. Protection against RSV must expand to lower-income countries, which are harder hit.
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