The measles outbreak continues to spread in the United States, surpassing 700 cases this year, federal health officials said on Monday. The virus has now been found in 22 states.
More than 500 of the 704 cases recorded as of last Friday were in people who had not been vaccinated, the Centers for Disease Control and Prevention reported. Sixty-six people have been hospitalized.
About 400 of the cases have been found in New York City and its suburbs, mostly in Orthodox Jewish communities. That outbreak has spread to Detroit.
Los Angeles is now experiencing a fast-growing outbreak, and hundreds of university students who are thought to have been exposed and cannot prove that they have had their shots have been asked to quarantine themselves at home.
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Last Wednesday, the C.D.C. said the number of cases had surpassed the previous high of 667, set in 2014. This year’s outbreak is the largest since the disease was declared eliminated in the United States in 2000. In 1994, there were 963 cases.
Elimination in 2000 meant measles virus was no longer circulating in the United States, as it presumably had since European settlers first brought it to this hemisphere in the 15th or 16th century. Each year after 2000, a few cases arrived from overseas, either in immigrants or in returning tourists, but each outbreak was snuffed out.
More than 94 percent of American parents vaccinate their children against measles and other diseases, Dr. Robert Redfield, director of the C.D.C., said on Monday.
His agency “is working to reach the small percentage of vaccine-hesitant individuals,” he said. “Vaccines are safe and do not cause autism.”
About 100,000 children in this country under age 2 have not been vaccinated, he said, meaning they are vulnerable in this outbreak.
Some infants are not immunized because their parents avoid vaccination. Others cannot be protected either because they are allergic to components of the vaccine or are, for example, taking cancer or organ-transplant medications that suppress their immune systems.
“We must join together as a nation to once again eliminate measles,” Dr. Redfield said.
This year’s widespread outbreak was sparked by people infected with measles who have come into this country since last year, the C.D.C. said. The measles strains detected were most frequently from Ukraine, Israel and the Philippines.
[Get answers to common questions about the measles outbreak.]
Communities have begun to take extraordinary measures to slow the infection rate and crack down on resistance to immunization.
New York City’s Mayor Bill de Blasio declared a state of emergency and threatened residents of four Brooklyn ZIP codes with $1,000 fines if they refused to vaccinate. City officials closed a yeshiva preschool for violating vaccination orders.
Rockland County, N.Y., the center of another outbreak, initially barred unvaccinated children from all indoor public places, including schools, malls, supermarkets, restaurants and houses of worship.
After a court blocked that order, the county instead barred from public spaces anyone who had measles symptoms or who had recently been exposed to the disease, threatening them with fines of up to $2,000 a day.
There have been no confirmed measles deaths in this country, but officials have said it is just a matter of time.
[Here’s our full coverage about the measles outbreak.]
Even with modern medical care, the disease normally kills about one out of every 1,000 victims, according to the C.D.C.
Pneumonia and encephalitis — swelling of the brain — are the most common severe complications, and epidemics among malnourished children who cannot get modern hospital care have mortality rates of 10 percent or more, according to the World Health Organization.
Measles is among the most contagious of diseases. Virus-laced droplets can hover in still indoor air for up to two hours after someone infected has coughed or sneezed. Up to 90 percent of people who are exposed will catch the virus if they are not immunized.
The vaccine is considered very safe, and two doses are about 97 percent effective at conferring immunity. The vaccine is normally given at ages 1 and 5, but during outbreaks pediatricians may give it to healthy children as young as six months old.
Around the world, measles cases fell 80 percent between 2000 and 2016, with deaths dropping to 90,000 a year from 550,000. But two years ago, cases began rebounding, driven by a combination of poverty, warfare, tight vaccine supplies and, in some countries, hesitation about vaccination.
Earlier this month, the W.H.O. said there were three times as many measles cases around the world this year as there were in the first three months of 2018.
Outbreaks of tens of thousands of cases have occurred recently in poor or war-torn countries like Madagascar, Ukraine and Yemen. But case numbers are also climbing in wealthy countries with modern health care systems, like Israel, Britain, France and Italy. Deaths from measles have occurred in those countries.
Before measles vaccination became widespread in the United States in 1963, up to four million Americans got measles each year, the C.D.C. said. Of the roughly 500,000 cases that were reported to medical authorities each year back then, about 48,000 were hospitalized, 4,000 developed encephalitis, and 400 to 500 died.
Nationally, since the mid-1990s, more than 91 percent of American children have been vaccinated against measles.
Anyone born before 1957 is assumed to have had the disease as a child and to be immune to it.
Americans born between 1957 and 1989 are in something of a middle ground. Some got the early “killed virus” vaccine, which later proved to be too short-lived and was replaced by a “weakened virus” vaccine. Until 1989, it was routine to give one shot; now children get two.
One shot of the new vaccine provides 93 percent immunity in the overall population, while two shots drive that up to 97 percent, which is considered more than enough to keep the virus from spreading.
But each individual’s immune system is different, so some Americans worried about the current outbreak have visited their doctors for a simple blood test that can show how immune they are to measles, mumps and rubella.
Immunization levels vary from state to state, largely dependent on how easy state legislatures make it to get exemptions. All states permit exemptions for children who are allergic to the vaccine, have a compromised immune system or have another medical reason to avoid it.
Some states permit religious exemptions, even though no major religion opposes vaccination, and a few states also permit “philosophical” or “personal choice” exemptions.
Only Mississippi, West Virginia and California allow solely medical exemptions; California previously had a very permissive law, but it changed it after the measles outbreak that began at Disneyland in 2014. Now the state has high vaccination rates among kindergartners.
Some states with high vaccination rates have “pockets of unvaccinated people,” the C.D.C. said. At various times, some religious minorities like Orthodox Jews and the Amish in Ohio have had low vaccination rates.
Some wealthy liberal communities, like Vashon Island in Washington State, have also had low rates. Recently conservative groups opposed to vaccines have sprung up, such as Texans for Vaccine Choice, which is associated with the Tea Party.
