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The United States declared victory over measles 25 years ago. And yet one of the worst outbreaks since then is ravaging Texas and New Mexico.
For now, it isn’t a threat to most Americans. But there’s a reason this is happening — and why the next measles epidemic could be even worse.
In today’s newsletter, I’ll explain the virus’s possible resurgence in America.
A map shows measles cases by county in 2025 through March 13. Outbreaks have been identified in Texas, New Mexico and New Jersey. Isolated cases have been identified in Washington, California, Oklahoma, Kentucky, Georgia, Pennsylvania, New York, Vermont, Rhode Island, Maryland, Georgia, Florida and Alaska.
Outbreaks
Isolated cases
Cases:
10
100
WASH.
VT.
N.Y.
R.I.
PA.
CALIF.
N.J.
MD.
KY.
OKLA.
N.M.
County not identified
GA.
TEXAS
ALASKA
FLA.
Outbreaks
Isolated cases
Cases:
10
100
WASH.
VT.
N.Y.
R.I.
PA.
CALIF.
N.J.
MD.
KY.
OKLA.
N.M.
County not identified
GA.
TEXAS
ALASKA
FLA.
Beating measles
Derailing this virus was a decades-long project. The United States began administering a vaccine in 1963, soon after its invention. At the time, the disease infected nearly all children before they turned 15.
Why did containment take so long? Because measles is one of the most contagious viruses on the planet.
In a hypothetical community where nobody has immunity, each person with measles can infect up to 18 others. But this graphic by my colleague Jonathan Corum shows what happens when enough people are vaccinated:
A diagram shows how measles can spread across a community, and how vaccinations help slow or stop the spread of the virus.
Outbreak
If each person with
measles infected 18
unvaccinated people,
a small outbreak
would quickly grow
out of control.
Herd effect
Every vaccinated
person slows the
spread of the virus
and helps reduce the
growth of the
outbreak.
Herd immunity
For an outbreak to
stop, each infected
person must infect
fewer than one other
person, on average.
In this example, 94
percent would need
immunity.
Outbreak
Herd effect
Herd immunity
If each person with measles
infected 18 unvaccinated
people, a small outbreak
would quickly grow out
of control.
Every vaccinated person
slows the spread of the
virus and helps reduce the
growth of the outbreak.
For an outbreak to stop,
each infected person must
infect fewer than one other
person, on average. In this
example, 94 percent would
need immunity.
A chart shows annual measles cases since 1985. In 1990, there were about 27,800 cases, and in 2000, there were just 85. In 2025 so far, there have been more than 300 cases.
25,000 cases
20,000
15,000
10,000
5,000
’85
’90
’95
’00
’05
’10
’15
’20
’25
25,000 cases
20,000
15,000
10,000
5,000
’85
’90
’95
’00
’05
’10
’15
’20
’25
