There have now been 880 measles cases reported in this year’s outbreak, already the largest since 1994, federal health officials said on Monday.
An additional 41 cases were reported last week, according to the Centers for Disease Control and Prevention. Of those, 30 were in New York State, which is having the country’s most intense outbreak, largely in Orthodox Jewish communities.
Most of those new cases were in New York City, and nine were in suburban Rockland County.
Cases have now been recorded in 24 states.
It is too early to tell whether the outbreak is slowing down, a C.D.C. spokesman said. In New York, transmission of the virus briefly appeared to slow in January, but then sped up in February.
An outbreak of geographically related cases is not considered to have ended until 42 days — two back-to-back 21-day incubation periods — have passed without a new case, the C.D.C. spokesman said.
Measles transmission tends to fade when warm summer weather arrives, other experts said. It is not clear whether that is because children are no longer gathered close together in school, because families spend less time indoors or because virus-laden droplets — like those containing influenza virus — stay airborne longer in cold, dry air than in warm, humid air.
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In the Pacific Northwest, which has been experiencing an outbreak unrelated to New York’s, immunization rates have jumped upward even on Vashon Island, Wash., which has long been known for its large number of parents who refuse to vaccinate their children.
Vashon, a haven for artists and organic farmers only 22 minutes from Seattle by ferry, has seen more parents accepting the vaccine for a combination of reasons, The Associated Press reported.
Many are worried about the outbreak, and some have taken advantage of efforts to make shots more available. Some residents are tired of the island’s reputation as the epicenter of vaccine rejection; the population is changing as wealthier commuters have moved in.
Vaccination rates among kindergartners in the island’s public schools rose to nearly 74 percent in 2018 from 56 percent in 2012, according to the county health department. That is still well below the 95 percent rate needed to assure that measles does not spread widely if it is introduced.
On May 10, Washington State got rid of the parental right to claim a “philosophical exemption” to the measles-mumps-rubella vaccine for schoolchildren. The law takes effect in July.
Washington’s outbreak has not reached Vashon Island; it is centered in Clark County, which is on the Oregon border.
