Bay Area public health officials urged the unvaccinated and immune-compromised to be cautious after a person with measles reported visiting several locations in Santa Clara and Alameda counties, but experts assured the public that most people have a “very high degree of protection” because of vaccination.

“Measles … is one of the most contagious diseases that we know about,” Dr. Sarah Rudman, acting health officer and director for Santa Clara County’s Department of Public Health said at a news conference Friday morning. “We know that the average person with measles can get up to 14 people sick, and you can imagine — 14 times 14 times 14 spreads incredibly quickly if the population is unvaccinated.”

Rudman added that despite the high rate of spread, the counties expect to be able to contain the disease due to high vatccination rates as long as individuals who were exposed follow public health recommendations.

After passing through an unspecified U.S. airport, the person visited the H Mart at 1710 Oakland Road in San Jose between 7:15 p.m. and 9 p.m. on May 21, the Starbucks at 35040 Newark Boulevard in Newark between 11:45 a.m. and 2 p.m. on May 23, and the Trader Joe’s at 1306 Great Mall Parkway in Milpitas between 4:45 p.m. and 8 p.m. on May 25, the Alameda and Santa Clara county public health departments said in a news release.

Members of the public may be at risk of getting measles if they visited the sites at those times and are not immune to the disease or are unsure whether they were vaccinated.

“The exact number of how many people have been exposed is unknown,” Rudman said. “That’s why we’re asking everyone to take a look at these three locations, the specific times when the contagious person was there — and if they understand that they were in that same location at that same time, they are considered exposed.”

Anyone who meets that criteria should review their immunization records to see if they are protected, and call their health care provider if they are pregnant, the parent of an infant, have a weakened immune system or are unvaccinated against measles. They should monitor for symptoms for seven to 21 days after the day of potential exposure, according to health officials.

Symptoms of the airborne disease include fever, cough, runny nose, conjunctivitis and a rash, which usually appears 7 to 21 days after exposure. Health officials urged anyone with symptoms to call ahead to their medical facility before seeking treatment.

Most members of the community have a “very high degree of protection and (are) very unlikely to get sick from that exposure” because of vaccination, Rudman added.

Dr. Kavita Trivedi, director of clinical guidance and communicable disease controller at the Alameda County Public Health Department, said that people who are exposed and exhibiting symptoms should immediately contact their healthcare provider. These individuals should be sure to call their doctor ahead of time so as not to expose other people in waiting rooms.

Health officials said the infected person may have been exposed to the disease at the airport. That person was not hospitalized and is isolating at home, according to health officials. The individual, who is an adult, is recovering well, Rudman said.

The most recent case of measles in Santa Clara County was in 2019, Rudman said. Alameda County had a case of measles in 2024, Trivedi said.

Trivedi added that the Bay Area has high rates of vaccination for measles, mumps and rubella.

“We’re very fortunate in the Bay Area to have the benefit of high vaccination rates,” Trivedi said. “Young children, unvaccinated children, unvaccinated adults, pregnant people and those with weakened immune systems are at greater risk for developing severe complications from measles.”

Trivedi added that the MMR vaccine is “safe and highly effective.

“Two doses of MMR vaccine is the best protection against measles,” she said.

Across the state, MMR vaccination rates dipped during the COVID-19 pandemic and have struggled to recover since. In Alameda County, MMR vaccination rates of kindergarteners dropped nearly one percentage point from the 2022-2023 year to 2023-2024. In Santa Clara County, the rates remained largely steady from 98.7% to 98.6% over the same time period.

California’s statewide MMR vaccination rate sat at 96.2% of kindergarteners, putting the state well ahead of a nationwide rate of 92.7%.

The United States has seen measles outbreaks in eleven states, with some 1,000 cases nationwide — triple the number from 2024. A recent Stanford University study predicted that measles could return to endemic level within two decades if current downward vaccination trends continued.

Rudman also expressed appreciation to the businesses who are cooperating with public health authorities to protect their staff and patrons. There is no further risk in going to these businesses now, she added.

More information about measles is available at sccphd.org/measles and acphd.org/measles.