Research shows immune system could be left in a temporary state of amnesia

The number of new U.S. measles cases continued to accelerate last week as health authorities race to curb the outbreaks and scientists who study the virus say measles may be more harmful than once believed.

There have been 555 cases of measles in 20 states across the U.S. this year as of April 11, the Centers for Disease Control and Prevention reported Monday, 90 more than were reported the previous week.

The increase in cases means 2019 could soon become the worst for measles in the U.S. since the disease was officially eliminated—meaning that it stopped circulating continuously—in 2000. In 2014, the worst year since elimination, 667 cases were reported.

The U.S. outbreaks this year are among the latest to emerge in developed countries, where high overall vaccination rates and access to health care make death from measles uncommon. Measles complications and deaths are a greater threat in poorer regions of the world, where inadequate nutrition and greater exposure to other infections can make it harder to fight off effects of measles.

The virus continues to flare up in the U.S. among groups whose vaccination rates are low, often after exposure to overseas travelers who return with the disease. An outbreak among Orthodox Jews in New York City this year has led to a surge in U.S. cases. New York City health officials said Friday that there have been 285 measles cases in the city, and more than 11,000 people have been exposed to the virus.

Researchers who study the virus say that concern about these outbreaks extends beyond the effect of the initial infection to longer-term implications for the health of the victims.

The virus may leave the immune system in a temporary state of amnesia, leaving the body’s defenses unable to remember and effectively attack some invaders it has seen before, according to emerging research. Immune-system memory loss could leave the body prone to more severe infections for two to three years, until it relearns from hard-won experience how to fend off attackers, researchers have said.

“You don’t have that quick response,” said Michael Mina, an assistant professor at Harvard University who studies immune-system response to the virus. “You have to create it from scratch again.”

Measles is highly contagious, infecting up to 90% of those who are susceptible. It can have complications and long-term effects. About one-third of children who develop measles will have complications, including diarrhea, pneumonia or ear infections. Some complications, though rare, are serious: about one in 1,000 people in the U.S. with measles develop encephalitis, or brain inflammation, that can develop a week or two after a rash appears and leave the victim deaf or with an intellectual disability. Read more at WSJ