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 Up to 10 percent of the 695 confirmed measles cases in the current
outbreak occurred in people who received one or two doses of the
vaccine, according to the U.S. Centers for Disease Control and
Prevention.
The figure illustrates what can happen when a large number of
individuals, even those who have been vaccinated, are exposed to the
measles. CDC recommends that people who are living in or traveling
to outbreak areas should check their vaccination status and consider
getting a new dose.
Dr. Allison Bartlett, an infectious disease expert at the University
of Chicago Medicine, said the “continued vulnerability to infection”
is why high-risk adults such as healthcare workers are routinely
advised to get a second dose of the measles vaccine if they have not
had one.
But knowing your vaccination status can be tricky, experts said.
“It’s complicated and often futile because it's very difficult to
resurrect those old records,” said Dr. William Schaffner, an
infectious disease expert at Vanderbilt University Medical Center.
People vaccinated in the United States since 1989 would most likely
have received two doses of the combined measles, mumps and rubella (MMR)
shot under federal guidelines, and that is still considered the
standard for protection.
Anyone vaccinated between 1963 and 1989 would likely have received
only one dose, with many people immunized in the earlier years
receiving an inactivated version of the virus. Americans born before
1957 are considered immune as they would have been exposed to the
virus directly in an outbreak.
Merck & Co Inc is the sole U.S. provider of the MMR vaccine. The
company said in a statement that it has “taken steps to increase
U.S. supply” of the vaccine due to the current outbreak.
HIGHLY CONTAGIOUS
The measles virus is highly contagious and can cause blindness,
deafness, brain damage or death. It is currently spreading in
outbreaks in many parts of the world.
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According to the World Health Organization, 95 percent of a
population needs to be vaccinated to provide “herd immunity,” a form
of indirect protection that prevents infection in people too young
or sick to be vaccinated. U.S. public health officials have blamed
the current outbreak in part on rising rates of vaccine skepticism
that have reduced measles immunity in certain communities.
For travelers to outbreak areas abroad, the CDC recommends adults
consider getting another dose of MMR unless they have proof of
receiving two prior doses, take a blood test showing immunity, or
were born before 1957.
In general, the CDC says two doses of the measles vaccine should
provide 97 percent protection; one dose should offer 93 percent
protection. However, immunity can wane over time.
This has occurred even in adults with two documented doses of the
vaccine, said Dr. Michael Phillips, chief epidemiologist at NYU
Langone Health, which serves parts of New York City, a hot spot in
the U.S. outbreak.
He said in kids, “the vaccine is really effective,” but in some
adults, memory T-cells, which recognize and attack germs, do not
fight the virus as effectively as they once did.
Rapid blood tests are available that can detect whether a person is
immune based on the level of measles antibodies, but the tests are
not 100 percent reliable.
Adults who have any doubt about their immunity should get another
dose, Schaffner said: "It's safe. There's no downside risk. Just
roll up your sleeve.”
(Reporting by Julie Steenhuysen in Chicago; Additional reporting by
Mike Erman and Gabriella Borter in New York; Editing by Lisa
Shumaker)
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