The nation's infant mortality rate dropped last year after two years of hovering at a late-pandemic plateau. Some experts think one reason for the drop could be a vaccination campaign against RSV, or respiratory syncytial virus, which is a common cause of cold-like symptoms that can be dangerous for infants. The infant mortality national rate dropped to about 5.5 infant deaths per 1,000 live births in 2024, according to the CDC. That's down from about 5.6 per 1,000 live births, where it had been the previous two years.