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By Julie Steenhuysen
April 28 (Reuters) – American adults vaccinated against measles decades ago may need a new dose depending on when they received the vaccine and their risk of exposure, according to reports. public health experts fighting the country's largest outbreak since the virus was considered eliminated in 2000.
According to the US Centers for Disease Control and Prevention, nearly 10% of the 695 confirmed cases of measles in the current outbreak occurred among people who received one or two doses of the vaccine.
The figure illustrates what can happen when a large number of individuals, even those who have been vaccinated, are exposed to measles. The CDC recommends that people living or traveling in epidemic areas check their immunization status and consider a new dose.
Dr. Allison Bartlett, an infectious disease specialist at the University of Chicago in Medicine, said that "continued vulnerability to infection" is why high-risk adults such as health professionals health are routinely asked to receive a second dose of measles vaccine if they have not already done so. had one.
But knowing the status of your vaccination can be tricky, experts said.
"It's complicated and often unnecessary, because it's very difficult to resuscitate these old recordings," said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center.
People vaccinated in the United States since 1989 would probably have received two doses of combined measles, mumps and rubella vaccine (MMR vaccine) in accordance with federal guidelines, which is still considered the standard of protection.
Anyone vaccinated between 1963 and 1989 would probably have received only a single dose, with many people having been immunized in the early years who received an inactivated version of the virus. Americans born before 1957 are considered immune because they would have been exposed to the virus directly in the event of an epidemic.
Merck & Co Inc is the only US supplier of MMR vaccine. The company said in a statement that it had "taken steps to increase the US supply" of the vaccine due to the current outbreak.
VERY CONTAGIOUS
The measles virus is highly contagious and can cause blindness, deafness, brain damage or death. It is currently spreading through hatching in many parts of the world.
According to the World Health Organization, 95% of the population needs to be vaccinated to provide "collective immunity", a form of indirect protection that prevents infection in people too young or sick to be vaccinated. US public health officials have blamed part of the current outbreak for increased vaccine skepticism, which has reduced immunity against measles in some communities.
For travelers traveling to outbreak areas abroad, the CDC recommends that adults consider taking another dose of MMR unless they have proof that they have already received two doses, to do a blood showing immunity or being born before 1957.
In general, the CDC says that two doses of measles vaccine should provide 97% protection. one dose should provide 93% protection. However, immunity can decrease with time.
This has happened even in adults with two documented doses of the vaccine, said Dr. Michael Phillips, chief epidemiologist at NYU Langone Health, which serves part of New York City, a hot spot of the American epidemic.
He said that in children, "the vaccine is really effective," but in some adults, memory-sensitive T cells, which recognize and attack germs, do not fight the virus as effectively as before.
There are rapid blood tests to detect a person's immunity based on the level of measles antibodies, but these tests are not 100% reliable.
Adults who have doubts about their immunity should be given another dose. Schaffner said: "It's safe, there's no risk, we're just lifting your sleeve."
(Report by Julie Steenhuysen in Chicago, additional report by Mike Erman and Gabriella Borter in New York, edited by Lisa Shumaker)
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