San Francisco Confirms First Measles Case Since 2019, in an Unvaccinated Infant

San Francisco public health officials on Wednesday announced the city’s first measles case since 2019, saying that an unvaccinated infant was exposed to the virus while traveling internationally.

The infant, who is younger than 12 months old, became infectious after returning to San Francisco and is currently recovering at home, the city’s Department of Public Health said in a statement. The case was confirmed on Monday evening.

All members of the infant’s household are reportedly vaccinated, the release said.

California is battling one of its worst measles outbreaks since 2019, with 39 confirmed cases this year as of noon Monday, before the San Francisco case was confirmed, according to the latest data available from the state’s Department of Public Health. No deaths have been reported.

Last month alone, nine related cases were reported in Placer and Sacramento counties, where officials said Wednesday that at least 19 cases have been confirmed amid an ongoing outbreak, including an exposure at a pediatric care setting. An outbreak is three or more related cases, according to the Centers for Disease Control and Prevention.

The rise in measles in the Golden State overlaps with a national resurgence of the preventable disease. In 2025, the U.S. reported its highest number of measles cases in 30 years, driven mostly by large outbreaks in Texas and South Carolina. The country declared measles eliminated in 2000, but that status is now at risk.

Jump straight to:

• When can babies get an early dose of the MMR vaccine?
• I’m planning to travel soon. How worried should I be about measles?

The virus, which is highly contagious, can cause serious illness and death. It spreads easily through the air when an infected person breathes, talks or coughs, and it can linger in the air for up to an hour. Symptoms can include fever, cough, runny nose and pink eye, followed 2-4 days later by a rash.

Two doses of the measles, mumps and rubella (MMR) vaccine are 97% effective at stopping illness, officials said. The standard MMR vaccine schedule involves two doses: the first at 12-15 months old and the second at 4-6 years old.

Dr. Susan Philip, San Francisco’s health officer, highlighted the risk as a reason to get vaccinated at any age.

“It is incredibly important to get the MMR vaccine, as measles is one of the most infectious diseases in the world,” Philip said. “If you and your family are traveling internationally, make sure everyone is up to date with the MMR vaccine and is aware of the symptoms of measles.”

Why is measles so dangerous for babies and children?

Measles is preventable with the combined MMR vaccine, and vaccination against the disease has been part of routine childhood immunization for decades. (There’s also a combined measles, mumps, rubella and varicella, or MMRV, vaccine, but it’s only licensed for use in children 1-12 years old.)

Babies and young children are especially at risk from measles, but because the measles vaccine is routinely recommended only for children 12 months and older, infants younger than 12 months of age — like the San Francisco child currently infected with measles — are especially vulnerable to infection.

For this reason, health officials usually advise parents of infants to reach out to their child’s health care provider before any international travel.

Parents intending to travel internationally with an infant may be able to secure an early MMR vaccination for children as young as 6 months old due to the measles risk they may face abroad if unvaccinated.

I’m traveling internationally soon. How aware should I be of measles?

Travelers are advised to stay up-to-date on the global locations where measles outbreaks are currently taking place. The CDC has a dashboard of these countries, which include India, Angola, Indonesia and Pakistan.

Anyone who is unvaccinated (or just doesn’t have “adequate evidence of immunity”) and planning to travel internationally in the coming weeks and months — even if not to a country with a current measles outbreak — can get an emergency two-dose course of the vaccine.

Domestic travelers should also know that there are measles outbreaks taking place in other U.S. states, including South Carolina, Texas, Utah and Florida.

Returning travelers should watch for any symptoms of measles for a total of three weeks after arriving back home.

If I’m vaccinated, could I still get measles?

Six years of living with COVID-19 have taught us that being vaccinated against a virus doesn’t necessarily mean you won’t get infected with that virus.

The COVID-19 vaccine, for example, does somewhat reduce your chances of being infected — although the CDC said that “protection against infection tends to be modest and sometimes short-lived” — but it also means you’re much less likely to get severely ill if you do get infected.

However, the measles vaccine is incredibly effective at protecting against infections, the CDC said, and two doses of the measles vaccine are “about 97% effective” at preventing measles if you’re exposed. (One dose is “about 93% effective.”)

As for why “about three out of 100” people vaccinated against measles will still get measles after exposure — also known as breakthrough cases — the CDC said that experts “aren’t sure why” and that this could be due to the responsiveness of an individual’s immune system to the vaccine.

“But the good news is, fully vaccinated people who get measles seem more likely to have a milder illness,” the CDC said — and fully vaccinated people “seem also less likely to spread the disease to other people.”

If I’m up-to-date on my measles vaccines, do I need a measles booster?

No. The CDC’s longtime advice says: If you had two doses of measles vaccine as a child according to the U.S. vaccination schedule, the CDC considers you “protected for life” and you “do not ever need a booster dose.”

But given that measles can be fatal to some people — and serious impacts from an infection can appear years later — even those who’ve had their MMR vaccine may be concerned about how protected they still are against the disease.

A simple blood test known as a “titer test” is a way medical professionals can see how much immunity a person still has against a disease like measles. Read more about how to check your measles immunity and who might need an extra MMR vaccine.