Nearly 300 students and employees at two Los Angeles universities were under quarantine Thursday due to possible exposure to the measles virus. The news comes as the US Centers for Disease Control and Prevention (CDC) reports the number of measles cases has spiked to at least 695 so far this year, the highest number since the disease was declared eliminated in 2000.

The University of California, Los Angeles (UCLA) said that 76 students and six faculty members remained quarantined as of Thursday afternoon after a student infected with measles attended classes on three days this month, the last on April 9. The quarantine was expected to last between 24 and 48 hours for most, but a few might need to remain in quarantine for up to seven days.

A California State University, Los Angeles spokesman also reported that 127 staff employees and 71 student employees had been sent home under quarantine orders after a measles exposure was thought to have occurred April 11 in a campus library.

The Los Angeles County Department of Public Health believes additional exposures may have occurred in April at Los Angeles International Airport.

According to the CDC’s new report, new cases of measles in New York, New Jersey and California the previous week have brought the total number of infections in the US to at least 695 so far this year. On Wednesday, New York City and suburban Rockland County confirmed an additional 37 cases of the potentially deadly disease.

Most of the cases are among unvaccinated children, although adults are also at risk. Cases in New York include two pregnant women diagnosed in mid-April. Measles during pregnancy can be dangerous for both the woman and her developing fetus, with a high risk of miscarriage, stillbirth, prematurity and low birthweight.

President Donald Trump felt obliged to urge parents to get their children vaccinated after the CDC announced the record number of measles cases across 22 states. “They have to get the shot,” the president told reporters Friday on his way to Indianapolis to address the National Rifle Association. “This is really going around now; they have to get their shot.”

Trump’s statement was at odds with earlier comments he has made on vaccinations. In a March 2014 tweet, he questioned why a child “gets pumped with massive shot of many vaccines” adding, “Healthy young child goes to doctor, gets pumped with massive shot of many vaccines, doesn't feel good and changes—AUTISM. Many such cases!”

During a Florida fundraiser in 2016, Trump spoke with a group of donors who are prominent proponents of the discredited link between vaccines and autism, including disbarred British physician Andrew Wakefield, the senior author of a now retracted 1998 Lancet study linking autism to the MMR vaccine.

The current measles cases can be traced to travelers returning to the US from countries where measles is still common. The virus can then spread rapidly, especially in a community with a high rate of unvaccinated individuals.

The majority of cases in New York, for instance, are traced to individuals returning from Israel and spreading the virus, particularly in the ultra-Orthodox Jewish community, where there is an insufficient vaccination rate to cause “herd immunity.” The CDC says herd immunity comes when the vaccination rate is about 95 percent. This means that the disease cannot spread very easily, even among those who can’t be vaccinated, like newborns and those with vaccine allergies.

The measles virus is airborne, transmitted by respiratory droplets from the nose, mouth or throat of an infected person. These small-particle aerosols from an infected person can remain suspended in air for long periods of time after a person has left a location. The virus can incubate in a person four days before the onset of the rash associated with measles, so people carrying the virus can spread it to others before even knowing they have the disease.

US health officials believed that the disease had been effectively eradicated in the US, because the vaccination rates were sufficiently high and no cases had been reported. The measles virus is given as part of the combination MMR (measles, mumps, rubella) injection. The CDC recommends that a child receive two doses: one at 12-15 months of age, and the second at four-six years.

However, the fractured state of the US public health system in the US allows millions of parents to be granted exemptions by states from having their children immunized—for medical, religious and “personal belief” reasons. In 2015, California outlawed all but medical exemptions after an outbreak of measles linked to the Disneyland amusement park.

A small but vocal group of parents across the country—clinging to debunked, antiscientific views—believe that vaccines, including MMR, cause autism, Attention-Deficit/Hyperactivity Disorder (ADHD) and other developmental problems.

In California, parents have sought and received exemptions for conditions from eczema to “medical fragility.” This places children with legitimate reasons for exemption—including newborns, those undergoing chemotherapy, the immuno-suppressed, those with life-threatening allergies—at danger.

Unscrupulous doctors have signed off on such exemptions. The Voice of San Diego reported last month that a single physician had written one-third of all medical exemptions from vaccination for children in the San Diego Unified School District.

With the measles outbreak spreading across the country, many people who previously never gave the disease a thought are trying to determine if they are at risk. The CDC considers an individual protected if they have written documentation that either (1) they are a school-aged child who received two doses of a measles-containing vaccine, (2) they are a preschool child who received one dose of the vaccine, (3) a laboratory confirmed that they had measles at some point in their life or that they are immune to measles, or (4) they were born before 1957 (when they most likely came in contact with the virus).

Finding these records, however, may be difficult, as there is no national organization that maintains vaccination records. The CDC makes some not-so-helpful recommendations on how to find them, including:

• Asking your parents or caregiver if they have your records;

• Looking through baby books and other filed-away documents;

• Checking with your high school and/or college health services. “Keep in mind,” the CDC notes, “that generally records are kept only for 1-2 years after students leave the system.”

• Checking with previous employers, including the military;

• Calling your doctor or public health clinic (who may have shut down, or not kept records);

• Contacting your state’s health department, where some states have Immunization Information Systems including adult vaccine registries.

The lack of a national public health entity to track all vaccinations, and a vigorous nationwide campaign to counter the pockets of the unvaccinated, poses the necessity of freeing the health of the population from the grips of the for-profit health system. This includes the pharmaceutical giants who develop and produce vaccines based on profit and the private insurers who determine how much out of pocket must be paid to receive them.

Before the measles vaccine was introduced in 1963 in the US, there were 4 million measles cases with 48,000 hospitalizations and 500 deaths in the US every year. It cannot be dismissed cavalierly as an innocent childhood disease.

Children under age 5 have the highest probability of death from measles, with pneumonia being the most common cause. Other less common complications include blindness, croup and severe diarrhea. Some children develop encephalitis, or swelling of the brain, which can lead to convulsions, mental retardation, or death.

Figures in the political establishment like Trump—who has courted the anti-vaccine zealots and spread their unsubstantiated and antiscientific claims while only commenting briefly when measles cases soared to record numbers—are placing the population in danger of the reemergence of measles and other diseases long thought to be eradicated in North America.