California is raising major concerns as measles, a highly contagious disease, rapidly spreads through areas with low vaccination rates.

“It’s astonishingly infectious,” stated Dr. Sharon Balter, who leads the Acute Communicable Disease Control Program at the Los Angeles County Department of Public Health. “It escalates quickly, and we can’t afford to delay action.”

Measles cases are climbing across the United States. By early March, the Centers for Disease Control and Prevention had confirmed over 1,200 cases nationwide for the year, with nearly 90% linked to active outbreaks.

Health officials in California and elsewhere report that outbreaks are emerging in communities where vaccination rates have decreased. For instance, in Shasta County, an unvaccinated child exposed hundreds to the disease at various public venues before being diagnosed, prompting a rigorous contact-tracing effort and heightened concern among local health officials.

Authorities emphasize the critical need for immediate action. “Every day is crucial,” Balter remarked, highlighting the importance of quick vaccination and increased public awareness as the disease continues to spread.

Measles can spread with alarming speed. When an infected individual enters a room, others lacking immunity can easily contract the virus simply by being present, illustrating the potential for rapid outbreak escalation in communities with low immunity levels.

The problem isn’t isolated. CDC data shows measles cases slipping back toward levels not seen in decades, a dramatic reversal from recent years when the virus was essentially eliminated from U.S. circulation.

Health leaders across the country are now scrambling to contain outbreaks and urge vaccination, warning that gaps in immunity could let this disease roar back in force.

Experts say one troubling issue: many U.S. clinics and hospitals have little to no real-world experience with measles.

“The generation of physicians who are currently, for the most part, treating patients haven’t actually seen what a measles case looks like other than from a textbook or a video,” Dr. Andy Lubell, chief medical officer of True North Pediatrics in Pennsylvania, told the New York Times last year.

Measles was declared eliminated in the United States in 2000 following widespread adoption of the vaccine, a public health triumph that cut cases from roughly 3 to 4 million annually to about 180, according to the CDC.

The message from experts is urgent, terse and unmistakable: act now or risk letting one of the most infectious diseases around tear even deeper into communities.