The number of measles cases in the United States has risen to 695, the highest annual number recorded since the disease was declared eliminated in this country in 2000, federal health officials said on Wednesday.
The total has now surpassed the previous high of 667 set in 2014, according to the Centers for Disease Control and Prevention. The virus has been detected in 22 states.
Most cases are linked to two large and apparently unrelated outbreaks. One is centered in Orthodox Jewish communities in New York City and its suburbs; that outbreak began in October and recently spread to Orthodox communities in Michigan.
The other outbreak began in Washington State.
“The longer these outbreaks continue, the greater the chance measles will again get a sustained foothold in the United States,” the C.D.C. said in a statement.
The virus mostly has stricken families that do not vaccinate their children, and the C.D.C. blamed “organizations that are deliberately targeting these communities with inaccurate and misleading information about vaccines.”
The agency appealed to Americans to seek advice from their family doctors instead.
[Get answers to common questions about the measles outbreak.]
The New York outbreak was set off by Americans who had visited Israel, where cases have been spreading in Orthodox communities since early last year. City officials have taken extraordinary measures to crack down on resistance to immunization.
Mayor Bill DeBlasio declared a state of emergency and threatened residents of four Brooklyn ZIP codes with $ 1,000 fines if they refused to vaccinate.
Twelve summonses have been issued so far, the city health department said; people who do not answer them can be fined $ 2,000. 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 believe it is just a matter of time. Dozens of victims — most of them young children — have been hospitalized.
[Here’s our full coverage about the measles outbreak.]
Two of the cases detected in New York City were in pregnant women, the city health department said. The virus can cause miscarriages or stillbirths.
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 those, 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.)
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, South Carolina and California allow only 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 right-wing groups opposed to vaccines have sprung up, such as Texans for Vaccine Choice, which is associated with the Tea Party.