San Francisco reports first measles case since 2019 in unvaccinated infant

San Francisco’s first measles case since 2019 has landed in an unvaccinated infant under 12 months old, a reminder that one airborne infection can move quickly through a dense city built around travel, transit and crowded indoor spaces. The child contracted the virus while traveling internationally and was infectious after returning to the Bay Area. San Francisco Department of Public Health officials said the infant is recovering at home, and vaccinated household contacts have lowered the immediate risk inside the home. The city is now reaching out to close contacts outside the household and urging anyone who may have been exposed to check vaccination records and speak with a health-care provider.

The public-health concern is not just the single case, but how easily measles can spread before people know they have been exposed. The virus can linger in indoor air for up to 2 hours after an infected person leaves a shared space, according to the Centers for Disease Control and Prevention. Early symptoms can start with fever, cough, runny nose and pinkeye, followed by a rash days later. Measles can also lead to pneumonia and encephalitis, and the CDC says about 1 in 5 unvaccinated people in the United States who get measles is hospitalized. Infants, young children, pregnant people and people with weakened immune systems face the greatest danger.

Health officials used the case to reinforce vaccination guidance that matters most for families planning travel. The routine MMR schedule calls for a first dose at 12 to 15 months and a second dose later in childhood, typically at 4 to 6 years. For infants 6 through 11 months old traveling internationally, the CDC recommends an early MMR dose before departure. Doses given before the first birthday do not count toward the routine two-dose series, which means children still need the standard shots once they are old enough.

The case is especially notable because it ended San Francisco’s measles-free stretch, with the last city case reported in 2019. In its March 2025 advisory, SFDPH said 97% to 98% of San Francisco children entering kindergarten had received all recommended measles doses, a level public-health officials say is high enough to help stop sustained spread. Even so, the city and the wider Bay Area have been warning for months that international travel raises the odds of exposure, especially with three major airports in the region. In March 2025, SFDPH noted 222 measles cases nationwide and three in California; in February 2026, California Department of Public Health clinicians were again told to watch for measles as cases rose. For San Francisco, the task now is the same one public health departments face every time a highly contagious disease appears: find exposures fast, notify people before they get sick, and keep one infant case from becoming a cluster.