Measles Came Through Union Station. Watch for a Fever Until October 3.

The county named a four-hour window. The shot that could have blocked this exposure has already timed out.

You're wondering whether this one is yours. It is if you were inside Union Station on Saturday, September 12, between 8 a.m. and noon. That four-hour window belongs to the Los Angeles County Department of Public Health, which published it on Friday after confirming that a visitor who turned out to have measles spent part of that morning in the building. And the first thing worth knowing is that the step most people reach for — go get a shot — stopped being able to help with this particular exposure on Tuesday. What's left is a date to hold on to, and it's October 3.

The window, exactly as the county wrote it

The department's September 18 notice names one place: Union Station, 800 N. Alameda St. The visitor arrived in Los Angeles on Amtrak's Southwest Chief, Train 3, on September 12, and left at 10:55 a.m. for Bakersfield on Amtrak Thruway Bus Route 5717. Anyone who was in the station that day between 8 a.m. and 12 p.m., the notice says, may be at risk of developing measles 7 to 21 days after being exposed. It puts the last day to monitor for symptoms at October 3.

Two things in that paragraph decide who this page is for, and both are worth slowing down over.

The window opens later than the train did. The county's notice gives a departure time and no arrival time. MyNewsLA, running City News Service's report, puts the Southwest Chief in at 7:03 a.m. If that's right, the county's window starts roughly an hour after the train got there, and nothing the department published explains the gap. Use 8 a.m. anyway. It's the department's line, it's the line its investigators drew, and it's the one a clinician will ask you about.

The window closes after the visitor had gone. Measles doesn't need the infected person to still be standing in front of you, which is the single fact that makes a four-hour window in a train station make sense. Here the county's own two documents put it two different ways in the same week. The press release says the virus "can stay in the air and on surfaces for many hours." The department's measles program page, updated the same day, says the virus can stay in the air for up to two hours. One sentence covers air and surfaces together; the other is about the air alone. We're printing both rather than picking, because either way the answer for a reader is identical: you did not have to see anyone to have been exposed.

Both documents agree on the other half of the timing, the part about the infected person. Someone with measles can spread it up to four days before their rash appears and up to four days after — which is why a notice can arrive a week after the morning it is about.

If you were on the train or the bus, a phone call may be coming

The station is the public exposure. The seats are handled separately. The notice says that passengers seated near the infected traveler on the train or the bus will be notified by their own local health departments, working with the Centers for Disease Control and Prevention. That is a list being worked through, not a verdict: if you rode Train 3 or Bus 5717 and nobody has called you, it doesn't mean you weren't near enough, and it doesn't mean you were. The station window above is the part you can apply to yourself today without waiting for anyone's phone call.

The shot that would have stopped it had 72 hours

The county's notice doesn't mention post-exposure treatment at all. The CDC's guidance for clinicians does, and it is the part of this calendar that has already gone by. For someone exposed to measles without evidence of immunity, the agency directs the MMR vaccine — measles, mumps and rubella — "within 72 hours of initial measles exposure," and immunoglobulin, an injection of donated antibodies, "within 6 days of exposure."

We counted forward from the county's own window. Seventy-two hours from Saturday morning ran out on Tuesday. Six days ran out on Friday. Both doors were shut before this page was written.

That is not an argument against getting vaccinated. It's a correction to what a shot today would do. A dose now does nothing about September 12 and everything about the next exposure, and the county's own list of notices says there keeps being a next one.

What you already have, and how to find out what that is

Two doses of the MMR vaccine are 97 percent effective against measles and one dose is 93 percent; the county publishes both numbers on its program page. If you've had measles before or had the recommended doses, the notice's language is that you are likely protected — and it still asks you to monitor. If you're unimmunized, or you genuinely don't know, you're in the group the department asks to watch closely.

"Don't know" is the common answer for adults, and there is a route out of it. The county's instruction is to request your record through California's Digital Vaccine Record request form and select the option for your California immunization record; its program page links the form directly. If your shots aren't in there, the department's next step is to ask the doctor, pharmacist or clinic that gave them to add them to the California Immunization Registry, the state's immunization database, which is where that form reads from.

What to watch for, and the call to make before you walk in

The county lists the symptoms in the order they tend to arrive: a fever over 101 degrees, a cough, a runny nose, red and watery eyes. Then tiny white spots inside the mouth, which clinicians call Koplik spots, two to three days after the other symptoms start. Then the rash, three to five days after the other symptoms start, beginning at the face and spreading down the body.

One line in the notice is written as an instruction rather than advice, and it is the one that protects everyone else in the waiting room. If symptoms develop, stay home, and call a health care provider — do not walk into a facility without calling first. Tell them you may have been exposed to measles and describe what you have. The point of the call is that they can decide where to put you before you are standing in a room with other patients.

Some people shouldn't wait for a symptom to make that call. The department names them: anyone pregnant, an exposed infant under 12 months, anyone with a weakened immune system, anyone unimmunized. For that group the instruction is to contact a provider about the exposure itself, as soon as possible. The stakes behind that line are on the program page, in the county's own figure: about one in five unvaccinated people in the United States who get measles end up hospitalized.

If you need the shot and don't have a doctor

Most health plans cover MMR, and a pharmacy is usually the fastest door. For anyone uninsured or underinsured, two programs carry the cost through the clinics enrolled in them: Vaccines for Children, for people 18 and under who are uninsured, underinsured, on Medi-Cal or eligible for it, or American Indian or Alaska Native; and Vaccines for Adults, for uninsured and underinsured adults 19 and over. The department's free and low-cost clinic lists are broken out by service planning area — the eight geographic zones the county runs its health services through — and were last updated September 16. Its Public Health InfoLine, 1-833-540-0473, reads the same list to you over the phone. We've already counted the 872 places in this county that give the school-required shots, and what closed at seven county health centers this fall, so this page won't re-list them.

The number this case isn't in

Los Angeles County's 2026 measles case count is seven, current through September 17. The Union Station visitor is not one of the seven, and the reason is a counting rule the county states on the same page: a case is counted by where the person usually lives, not by where the exposure happened. A visitor who was infectious here belongs to whichever jurisdiction is investigating them.

So the county's case number and the county's exposure notices are measuring two different things, and the second is the one a reader in this county is actually inside of. We counted it off the department's own list: eleven measles press releases in 2026, the September 18 notice included, running from January 30 to Friday.

The national figures in the same release are the county's reason for sending it. As of September 18, the notice says, 3,471 measles cases had been reported in the United States this year, resulting in four measles-associated deaths, across 39 new outbreaks. Nine percent of those cases needed hospital care.

The rest of the trip, for anyone who kept going

The California Department of Public Health issued the wider notice the same week, covering the whole route rather than the one station. The state's own website returned a server error to us on both attempts, so this paragraph is credited to the outlets that carried the state's list rather than to a state document we read. CBS News Sacramento and KTVU both report that the traveler was unvaccinated and is now hospitalized, and that the trip ran from Chicago to Los Angeles on September 10 to 12 and on to Denver by September 15, touching six California counties along the way: Los Angeles, Kern, San Joaquin, Butte, Sacramento and Alameda. Both outlets put California's year at 59 measles cases in 13 counties as of September 14, with 94 percent of them in people who were unvaccinated or whose vaccination status wasn't known. Rita Nguyen, the assistant state public health officer, told both outlets that measles "is one of the most contagious infections that can lead to severe life-long consequences, including permanent brain damage."

If you boarded or got off at Bakersfield, Stockton, Oroville, Sacramento or Emeryville in that stretch, the county health department where you live is the one publishing your window, and it will not be the four hours above.

Do it in this order

First, settle whether you were in it. Inside Union Station, Saturday September 12, between 8 a.m. and noon. Not the parking structure, not the bus plaza the notice doesn't name — the station, in those hours. If you weren't, this page is a bookmark and nothing more.

Then put October 3 in your calendar. That is the county's last day to monitor. Symptom-free past 21 days and you are no longer considered at risk, in the department's own words.

Check what protection you have, today rather than at the first fever. Request the state record if you don't know, and ask your provider to file any doses that are missing from it.

If you're pregnant, live with an infant under a year, or your immune system is suppressed, call a provider now — about the exposure, not about a symptom. That call is the one the department asks for up front, and the treatment windows that have closed are exactly why it is worth making early rather than on schedule.

And if a fever and a cough turn up before October 3: stay home, phone first, say the word measles, and let them tell you which door to use.