As a measles outbreak erupts in Texas and New Mexico, vaccination rates for the highly contagious disease have struggled to recover in California since they dipped to worrisome levels during the pandemic.
The outbreak of at least 146 cases and counting in Texas and 9 in New Mexico has also led to twenty hospitalizations and the first measles death in the United States in a decade. A school-aged child, who was unvaccinated, died this week from the disease.
Measles was declared eliminated in the U.S. in 2000, due to a highly effective vaccine and public health campaigns.
“The measles vaccine is very effective,” said Dr. Monika Roy, assistant health officer for Santa Clara County. “One dose is estimated to be 93% effective, and in two doses 97% effective.”
However, the virus is reintroduced through international travel periodically, with 16 outbreaks reported nationwide in 2024, according to the Centers for Disease Control and Prevention. Experts agree that a high vaccination rate is the best protection against the virus’ spreading, with 95% considered a safe threshold, but public health officials have long struggled to maintain vaccination rates above that threshold.
“It’s one of the most, if not the most, transmissible infectious agents we know,” said Peter Chin-Hong, a UC San Francisco professor of medicine. “Before the vaccine, we normally saw about 500 dead kids and 1,000 disabled kids a year from measles in the U.S.”
California’s most recent big outbreak made international news when over 100 measles cases were reported, linked to an exposure at Disneyland in December 2014. “Somebody can go into a room (with measles), leave the room, and two hours later you go in the room, if you’re unvaccinated you’ll catch measles,” said Chin-Hong.
Vaccination rates in California got a boost after the Disneyland outbreak spurred legislation that reduced the number of legal exemptions California families could get in lieu of vaccinating their children before sending them to school.
Before the pandemic, the rate of kindergarten students who received their measles, mumps and rubella vaccination had reached just over 98% statewide.
Amid the pandemic disruptions and increased skepticism about vaccines, the percentage of kindergarten students vaccinated against measles dropped to 95.1% around the state in the 2020-21 school year but grew by over a percentage point the next year, and another two-tenths of a percent in 2022-23 to 96.5%, still remaining below pre-pandemic levels.
In the four years before the 2020-21 school year, between 1% and 1.5% of kindergarten students were overdue for at least some of their required vaccines, but that number jumped to 4% in 2020-21.
While California was able to avoid dropping below the 95% threshold as a whole, several counties in the state have rates below 95%. In the Bay Area, 54 schools have reported rates under 95% among kindergarten students, and another three did not report the data for the 2023-24 school year, according to an audit form the California Department of Education.
The state education department released a list of 375 schools around that state that reported over 10% of kindergarten students with conditional or overdue vaccination status for the 2023-24 school year. Of those schools, 31 are in Alameda County, all but one in Oakland Unified School District. Another seven schools in Contra Costa County were on the list, six in San Francisco, eight in Santa Clara County and two in San Mateo County.
Roy said the health department does not have comprehensive data on vaccination rates for all residents but does have data on vaccination rates among children. She said the vaccination rate countywide is over 95%, and no school district has a rate below that, adding that the county health department helps the schools report their vaccination data to the state.
Last year, the California Department of Public Health reported 15 measles cases and four in 2023. No cases were reported in January of this year, but three have been reported in February around the state.
Los Angeles County and Orange County public health departments announced a local case and possible exposures this week after a child who lives in Orange County traveled abroad and returned while infectious through LAX airport.
“The single most important thing is make sure you are up to date on your measles vaccine,” Roy said. “And that’s more important if you’re planning to travel internationally.”