An unnamed woman from Placentia, California, may have exposed attendees of Thursday’s Avengers: Endgame midnight premiere to measles.

The woman in question reportedly contracted the highly contagious virus while overseas, and unknowingly brought it with her to the midnight premier of Avengers Endgame, Marvel’s record-shattering blockbuster in Fullerton, California. According to authorities, anyone who attended the AMC movie theater on Lemon Street between 11 p.m. Thursday and 4 a.m. Friday may have been exposed.

The woman also exposed her workplace and a hospital emergency room to the virus, over the course of several days. She joins 704 cases confirmed across 22 states in 2019. Los Angeles country officials officially declared a measles outbreak last week.

“Measles is a highly contagious and potentially severe disease that causes fever, rash, cough and red, watery eyes,” Orange County interim health officer Dr. Nichole Quick told the LA Times in a statement. “The MMR vaccine is a simple, inexpensive and very effective measure to prevent the spread of this serious virus.”

Measles cases are now the highest on record since the disease was declared eliminated nationwide. Most outbreaks center on areas with low rates of vaccination. Despite the unfounded but recently popularized superstitions about their risks, the medical community has stressed that MMR vaccinations are vital to the prevention of this potentially deadly disease.