Tens of thousands of commuters may have been exposed to measles after an person infected with the highly-contagious virus traveled by train into and out of San Francisco last week, county health officials said on Wednesday.
Health officials in Contra Costa County, CA, issued an advisory to riders of San Francisco’s Bay Area Rapid Transit (BART) system on Wednesday after confirming the area’s first case of measles since a massive outbreak began in California in December and quickly spread across the US. The infected employee rode BART trains between Lafayette and San Francisco during the morning and evening commutes Feb. 4 through Feb. 6., officials said. The infectious employee also went to a restaurant (E&O Kitchen and Bar) in San Francisco last week.
According to the San Francisco Chronicle, the rider worked at LinkedIn. Officials at the social networking site – based in the Silicon Valley suburb of Mountain View, which is also home to Google – told the Chronicle they were notified on Tuesday that one of their workers had been infected with measles. The company said it notified all employees that day, alerting them of the risk of exposure.
Health officials said they are tracing the infected rider’s movements and contacting all those who may have been potentially exposed. “We’re trying to figure out who that person is in contact with,” Erika Jenssen, the head of the communicable disease program in Contra Costa, told the Chronicle. “With measles it’s a little more difficult” than with other infectious diseases because the virus is so contagious, she said.
Public health authorities stressed that the risk of infection is, in general, low because most people are inoculated against the virus, and the vaccine is highly effective. However, those who have not been vaccinated “are at high risk” of coming down with measles if they came into contact with the BART commuter, officials said. According to the Centers for Disease Control and Prevention, the measles virus is so contagious that 9 out of 10 people who have close contact with a measles patient will become infected themselves, unless they are vaccinated.
The state Department of Public Health said it does not know how many San Francisco Bay Area residents are fully immunized against measles. The number of parents declining to vaccinate their children has risen in the region — and the country — in recent years, though vaccination rates remain above 90% nationwide. In California, 11 percent of kindergarten students — about 13,000 children — have not been vaccinated against measles, but that figure rises to more than 60 percent at some private schools in the state.
Children who attend daycare facilities run by top Silicon Valley tech companies seem to have comparatively low vaccination rates, according to an investigation by Wired using data from the California department of public health. Wired found that the level of vaccination coverage at half of the 12 companies it surveyed – including Google, Yahoo and IBM – was below the threshold required for herd immunity, which is critical to preventing the spread of measles (and other diseases).
In order for any vaccine to be effective, a certain percentage of people in the population must be immunized. When that threshold is reached, most members of the population are protected because there is little opportunity for disease transmission. Importantly, the protection of herd-immunity extends even to those who cannot be vaccinated—such as infants, pregnant women, or immunocompromised individuals—since the spread of contagious disease is minimized.
For a highly contagious disease like measles, the threshold for herd immunity is around 90 to 95 percent. But the moment measles vaccination rates fall below that critical threshold, the disease can find enough hosts to spread in the community. That’s what happening right now in California, where clusters of underimmunization have allowed diseases to gain the upper-hand. In just the last month, the state has confirmed at least 107 cases of measles in an outbreak traced to an unvaccinated traveler at Disneyland. Nationwide, more than 120 people in at least 17 states and Mexico have been infected with measles in 2015.
“[This outbreak] highlights the need for people to be vaccinated,” Jenssen said in a statement from Contra Costa Public Health. “This is just another example of how interconnected our region is and how important it is for everyone to be up to date on their immunizations.”
Meanwhile, health officials in Nevada warned Wednesday that anyone who ate last week at a top-name Las Vegas Strip restaurant should review their immunization status and contact their health care provider if they are not fully immunized against measles and have not already had the disease. Tests confirmed this week that a child and an adult have measles, bringing to four the number of cases reported since the beginning of the year in and around Las Vegas, the Las Vegas Sun reported. The adult, who wasn’t fully vaccinated, works at Emeril’s New Orleans Fish House at the MGM Grand Hotel & Casino, and may have exposed people who dined at the restaurant after 4 p.m. between Wednesday, February 4 and Saturday, February 7.
Health officials declared measles eradicated in the United States in 2000, due in large part to the widespread use of the vaccine. Though the vaccines are said to be 99% effective, a recent anti-vaccination movement in the US – linking autism to the vaccines, even though that link was debunked in at least 107 independent scientific studies – has seen an increase in the number of parents who choose not to vaccinate their children. The subsequent spike in measles cases is no coincidence. In fact, epidemiological data from recent measles outbreaks reveal that the vast majority of cases since 2008 have occurred in communities with vaccination rates that were far below average.
The American Academy of Pediatrics released a statement last month urging parents, schools and communities to vaccinate children against measles. The group said all children should get the vaccine for measles, mumps and rubella (MMR) between 12 and 15 months of age and again between 4 and 6 years old. According to the CDC, two doses of the MMR vaccine are about 97 percent effective at preventing measles.