SEATTLE -- Think you’re immune to measles? If you’re like most adults in the United States, you probably aren’t entirely sure.
The U.S. Centers for Disease Control recommends a single dose of the measles vaccine to most people. But, a small portion of people given the shot don’t get immunity from it, and some vaccines given decades ago have since been proven ineffective.
With three exposure incidents in King County this summer and a recent outbreak in Texas, health officials say some people could benefit from another dose of the vaccine.
The measles vaccine is recommended to anyone born after 1957, while anyone older than that is believed to have already been infected. Of those who receive one dose of the vaccine, 5 percent will not be immunized, though they likely don’t know it. For this reason, a second dose of the vaccine, and a second chance at immunity, is recommended to people who are at higher risk of contracting measles, including healthcare workers, people who travel internationally and students.
The CDC also recommends people who were vaccinated between 1963 and 1967 get a second vaccine, because their first one may have been ineffective. During these years many doctors administered vaccines with inactivated (killed) viruses, which were later found not to result in measles immunity.
Dr. Chia Wang, an infectious disease specialist at Virginia Mason, decided to get vaccinated again as an adult because she does not know if she received a live or killed vaccine during the 1960s.
“Most of us don’t know which vaccine we received,” Wang said.
The only way to know if you are immune to measles is through a blood test, but Wang said it is easier to simply get another dose of the vaccine.
“There’s no downside to getting an extra vaccine,” she said. “If in doubt, just go ahead and get it.”
With children, Wang said parents are typically more aware of immunization status. But in cases where parents choose not to vaccinate, she said families need to be aware of measles symptoms, especially if the plan to travel to areas with greater measles incidence. The Netherlands just experienced a measles outbreak last month.
Despite recent exposure incidents, Betsey Hubbard of King County Public Health said King County residents are typically not at risk of measles.
“We don’t have measles in this county as a regular thing,” she said. “It’s usually an imported thing. The regular person wandering around King County doesn't need to be worried about measles.”
Still, the county’s low risk is credited to immunity among the general population. If the majority of local residents do not continue to get vaccinated, the safety of immune-compromised residents, including pregnant women, could change.