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When a possible measles case is identified in California, a phone rings at the local health department and the clock starts ticking.

Laboratory workers need to process samples as soon as possible to confirm the case. And a public health nurse must call the patient to find out where they’ve been and who they’ve been in contact with recently.

If test results are positive, the communicable disease team has 72 hours or less to identify anyone who has been exposed and may be at high risk of infection or serious illness. Those people must quarantine or take a dose of a post-exposure prophylaxis to prevent spread. For the next 21 days nurses will monitor the group for symptoms.

Measles is the most contagious vaccine-preventable viral infection in the world, and California is fighting multiple outbreaks. In a room where one person is infected, nine out of 10 unvaccinated people will also contract the disease. The viral particles also linger in the air long after the contagious person leaves, risking exposure to those who enter the room up to two hours later.

“That’s ridiculously infectious,” said Dr. Sharon Balter, director of acute communicable disease control with Los Angeles County public health. “It balloons very quickly, and because measles spreads very fast we have to get on it right away. We can’t say we’ll wait until tomorrow.”

California has a high enough vaccination rate — about 95% of kindergarteners — to provide herd immunity against measles, but throughout the state pockets of unvaccinated communities drive outbreaks, experts say.

Shasta and Riverside counties are working to contain localized outbreaks. These are the first measles outbreaks in the state since 2020 and are happening at a time when health departments have less money and fewer staff than in recent years. In total, seven counties have reported a total of 21 measles cases this year, according to the California Department of Public Health.

Throughout the country, 26 states have reported measles cases since the start of the year, including a massive outbreak in South Carolina where officials identified nearly 1,000 cases, mostly among unvaccinated children. It is the largest outbreak since theCenters for Disease Control and Prevention declared measles eradicated more than 25 years ago.

“The United States is experiencing the highest numbers of measles cases, outbreaks, hospitalizations and deaths in more than 30 years, driven by populations with low vaccination rates,” said California Public Health Officer Dr. Erica Pan in a statement earlier this month. “We all need to work together to share the medical evidence, benefits, and safety of vaccines to provide families the information they need to protect children and our communities.”

Containment comes with high costs

Investigating any communicable disease is time-intensive and expensive. The first three measles cases reported in L.A. County this year cost an estimated $231,000, according to a health department analysis.

Why does it cost so much? Because a disease investigation often requires a legion of public health nurses, physicians, epidemiologists and laboratory scientists to follow-up with hundreds of contacts, Balter said.

A computer shows an analysis of measles sequencing results at the Los Angeles County Department of Public Health laboratory in Downey on Feb. 26, 2026. Photos Ariana Drehsler for CalMatters

That includes sometimes visiting homes or exposure sites. For example, a recent exposure at a daycare required nurses to wring urine out of used diapers to test babies for measles. County health workers monitored 246 people who had been exposed to those first three measles cases — and the work is ongoing.

On Feb. 19, the county reported its fourth measles case. All of them were related to international travel. Other cases in California also have primarily been related to travel either internationally or to states where there are outbreaks. An unvaccinated child in Napa County contracted measles in January after traveling to South Carolina.

Riverside County health officials reported one measles case where the child had not traveled recently, and Shasta County health officials suspect their first case could be related to travel in Southern California but are waiting for DNA testing for confirmation.

Orange County reported two travel-related cases this year.

Health departments have fewer resources, more cases

Local health departments rely heavily on federal funding to prevent the spread of infectious diseases, but last year, the Trump administration slashed nearly $1 billion of public health funding from California. This year it attempted to claw back another $600 million from California and three other Democratic states.

Pending lawsuits froze the cuts, but local health departments are treating the money as a lost cause because they cannot bear the financial risk if a judge eventually rules in favor of the Trump administration.

Consequently, health departments closed clinics, terminated programs and laid off dozens of workers.

“What we can do with less is less unfortunately,” Balter said. L.A. county is facing a $50 million shortfall due to federal, state and local cuts and recently closed seven public health clinics.

Health departments are also confronting decreased public confidence: The high-profile questioning of vaccine safety and effectiveness by U.S. Secretary of Health and Human Services Robert F. Kennedy Jr. has complicated public health’s struggle to contain the spread of preventable infections.

California Democratic leaders are aggressively fighting Kennedy’s direction. They sued to block the administration’s new vaccine guidelines, which stripped universal recommendation from seven childhood vaccines. They blame Kennedy and the Trump administration for “dismantling” the Centers for Disease Control and Prevention and stoking fears over debunked claims that vaccines cause autism.

The state also released its own vaccine guidelines and formed an alliance among four western states to share public health information and recommendations.

“Everything including the outbreaks, the financial cuts, the questions from the federal government that are arising are making our work very difficult,” said Dr. Regina Chinsio-Kwong, Orange County public health officer.

Lab Assistant Abraham Jimenez loads blood samples for automated serology testing for measles immunity status at the Los Angeles County Department of Public Health laboratory in Downey on Feb. 26, 2026. Photo by Ariana Drehsler for CalMatters

Twelve years ago, Orange County was the site of California’s largest measles outbreak in decades. An exposure at Disneyland from an unknown source infected 131 Californians and spread to six states, Canada and Mexico.

The outbreak, which lasted four months, spurred state lawmakers to pass some of the strictest childhood vaccine requirements in the country.

But even a single measles case requires “vast amounts of infrastructure” to contain, Chinsio-Kwong said. On average, the department identifies and monitors 100 exposed people per case. Since the start of last year, Orange County has lost $22 million in federal cuts to public health. The department is trying to protect their communicable disease surveillance work, but it gets harder with every cut.

“We’re trying to prioritize our communicable disease control division,” health officer Chinsio-Kwong said. “There are a lot of different federal cuts, but we’re putting that as front and center: That has to be saved no matter what.”

Measles spread in unvaccinated groups

Six hundred miles north, Shasta County is grappling with its first measles cases since 2019 and the state’s largest outbreak of the year.

In late January, a sick child visited a health clinic in Redding with measles symptoms that laboratory testing later confirmed. Health officials interviewed 278 people and identified six locations where others were exposed: a restaurant, a church basketball game, a gym, a park, Costco and the clinic.

They also identified seven other cases among family members or neighbors who were in close contact with the child.

It can take 21 days from the time of exposure for measles symptoms to develop. On Feb. 19, just before the end of that period, health officials confirmed a ninth case.

That person didn’t recognize the symptoms and visited several places while contagious, including a school, a church service, a basketball game and a clinic, said Daniel Walker, a Shasta County supervising epidemiologist. Now, the contract tracing process has started over. The communicable disease team expects to interview even more people this time.

All cases have been among children who were unvaccinated or did not know their vaccination status.

“It’s a great time to get immunized, because you can’t know when you’re next going to be exposed…especially because we’re in an outbreak situation,” Walker said.

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Supported by the California Health Care Foundation (CHCF), which works to ensure that people have access to the care they need, when they need it, at a price they can afford. Visit www.chcf.org to learn more.