Ventura County health officer briefs Oxnard Council on measles risks, prevention

Dr. Aldine Castell, Ventura County Health Officer, told the Oxnard City Council on Sept. 16 that measles remains a public-health concern because the virus is extremely contagious even though it is largely preventable with vaccination. "If 1 person has this virus in a room of 10 people, 9 people who are not vaccinated or protected will walk out being infected," Castell said, adding that two doses of MMR vaccine provide roughly 97% protection.

Castell said the county is watching measles closely as a possible sign that vaccination rates for other preventable diseases may be falling. "We in public health see measles like a canary in the coal mine," she said. She reviewed national and local trends, noting that the United States has reported a rise in measles cases in 2025 and that 92% of cases reported this year were unvaccinated people or had unknown vaccination status.

Why it matters: measles can cause serious complications, Castell said, including hospitalization and, rarely, fatal outcomes or delayed complications such as subacute sclerosing panencephalitis. She told the council that infants and people with weakened immune systems are most at risk, and that community ("herd") immunity of about 95% is required to prevent sustained transmission.

Local picture and response: Castell said Ventura County’s kindergarten MMR rates remain above the 95% threshold and are higher than statewide averages, but she urged continued vigilance. County public-health work includes provider engagement and advisories, bilingual public education and reminders, cooperation with school nurses at Ventura County Office of Education, lab readiness and surge plans with EMS partners, and plans for case investigation and contact monitoring in the event of a local case.

Council questions and answers: Council members asked whether the county maps areas of lower vaccine coverage and how outreach is targeted. Castell said the county monitors kindergarten vaccine rates and reaches out to schools with lower-than-expected coverage to offer assistance, including vaccine clinics when funding and logistics permit. She said schools may allow a short grace period for required immunizations, and that medical exemptions are handled through the student’s physician.

Castell advised residents who see the classic measles rash—"it always starts in the head and moves down"—to contact their medical provider and isolate while testing is arranged. She closed by urging residents to "stay up to date with their vaccines and support vaccination and the messaging surrounding that to your communities, to your family, and to your loved ones."