Multiple measles cases confirmed in California infants, including first San Francisco case since 2019

California health officials confirmed multiple measles cases in 2025, including a baby under 1 year old in San Francisco marking the city's first case since 2019, a 7-month-old in Orange County, and other cases bringing the state total to 48 confirmed infections. The infants were too young to receive the standard MMR vaccine typically given at 12-15 months, highlighting the vulnerability of babies who depend on herd immunity for protection. With 1,814 measles cases confirmed nationwide in 2025 and 92% occurring in unvaccinated or unknown-status individuals, the outbreak represents a dramatic surge from the quarter-century when measles was considered eliminated in the United States. The disease poses severe risks including SSPE, a fatal brain condition affecting as many as 1 in 600 babies infected with measles, which killed a Los Angeles County child in September 2024 who had contracted measles as an infant.

Recent measles cases in California infants

• ▪The San Francisco measles case was the first in that city since 2019
• ▪Orange County reported a confirmed measles case in a toddler in January 2025
• ▪A baby under 1 year old in San Francisco was infected with measles in early 2025
• ▪A baby in Orange County, California contracted measles in 2025

Health risks and complications of measles in young children

• ▪A school-age child in Los Angeles County who had contracted measles as an infant died of SSPE in September 2024

Vaccination recommendations and early immunization strategies

• ▪One dose of the MMR vaccine is 93% effective at preventing measles
• ▪95% measles vaccination coverage is the threshold considered necessary for herd immunity
• ▪A second dose of the MMR vaccine boosts effectiveness to 97%
• ▪The CDC and California Department of Public Health recommend that everyone 12 months or older receive two doses of the measles vaccine before traveling internationally

National measles surge and declining vaccination rates

• ▪4% of confirmed measles cases in the United States so far in 2025 had received just one of the two recommended MMR doses
• ▪A 28-year-old immunocompromised adult died from measles in the United States in 2015
• ▪A 13-year-old immunocompromised child who recently had a bone marrow transplant died from measles in the United States in 2003
• ▪A 75-year-old infected in Israel who suffered measles pneumonia and brain damage died in the United States in 2003
• ▪92% of confirmed measles cases in the United States so far in 2025 have been individuals who were unvaccinated or whose vaccine status was unknown
• ▪The United States had seen only three total measles deaths over the quarter-century preceding 2024
• ▪An unvaccinated adult in New Mexico died from measles in 2024 or 2025
• ▪2,288 measles cases were documented in the United States in 2024
• ▪1,814 measles cases have been confirmed nationwide in the United States so far in 2025