Measles is on the rise in the United States, the Centers for Disease Control and Prevention said last week. And Allegheny County, with two cases this year, is not immune to the trend.
But it's not completely following it, either.
Nationally, most of the 288 measles cases reported between Jan. 1 and May 23 have been associated with unvaccinated people, according to the CDC. But here Allegheny County, the two reported cases both involved people who said they had received measles vaccination, yet still caught the highly contagious respiratory disease.
"There's always going to be some people who don't mount a response to the vaccine," said Karen Hacker, director of the Allegheny County Health Department. Or their immunity may have waned with time, she said.
But most people who received the recommended two doses of the mumps-measles-rubella (MMR) vaccine will be protected, she said. The high rate of vaccination among residents of Allegheny County has helped prevent the disease from spreading, although Dr. Hacker said that based on the CDC report, she anticipated the county would see additional cases.
"I think people have a lot of respect for vaccines here," said Amesh Adalja, an infectious disease physician for UPMC.
Measles continues to afflict residents of other countries in large numbers, but the 288 cases reported by the CDC represent the highest five-month total of measles cases in the United States since 1994. Prior to the vaccine's development in the 1960s, there were 3 million to 4 million measles cases each year, according to information provided by the CDC.
Successful vaccination efforts led U.S. officials to declare the disease had been eliminated by 2000, but the CDC still reported about 60 cases a year until recently, when the numbers increased, both due to people not being vaccinated and international travel, the agency said.
The relative rarity of measles cases in the United States, compared to the prevalence a few decades ago, means that people do not experience the "natural boosting" that, along with the vaccine, help the body to protect itself from measles, Dr. Adalja said. And that might explain why, here in Allegheny County, two people who received the vaccines still developed the measles, he said.
"Your immune system hasn't seen anything looking like measles for decades, so the vaccine is not going to be as effective," he said. But vaccines are still the most effective way to prevent measles, he said.
The CDC recommends two doses of the MMR vaccine starting at age 12 months. There is no risk for getting an additional dose of the MMR vaccine, but Dr. Hacker said health officials are not recommending it.
"We adhere to the CDC recommendations, and if an individual has had two vaccines, we have no current guidelines to suggest they do anything different," she said.
Kaitlynn Riely: firstname.lastname@example.org or 412-263-1707.