A record number of measles cases is hitting the U.S. this year. Who is being affected?

The rising number of measles cases this year is by far the most since successful vaccination led to elimination of the disease in this country almost two decades ago. Cases appear in the United States every year when travelers bring it into the country.

At least 971 cases have been reported this year across 26 states, according to the Centers for Disease Control and Prevention. The ongoing major outbreaks may soon mean measles can no longer be considered eliminated from this country, the agency said.

Declining vaccination rates have increased the risk of outbreaks when the virus arrives, and allowed it to persist in some communities.

Measles cases by county

Travel can spread measles quickly from one community to another. A child who flew to the United States from Israel brought measles into Brooklyn, public health officials said, and then an infected member of that community drove to Michigan, creating an outbreak there. Outbreaks have also branched out from Brooklyn to other parts of New York, Connecticut and Baltimore County. An outbreak in New Jersey may also be related.

Measles cropped up in Los Angeles this year after a traveler brought it home from Vietnam. Then a second traveler brought it from Thailand. California’s largest outbreak — near Sacramento — came from a visitor to the Philippines, according to state health officials.

The vast majority of people infected have not been vaccinated. Communities with lower vaccination rates are vulnerable because measles spreads so quickly through coughing and sneezing.

A historic number of cases in decades

Before the measles vaccine was introduced in 1963, experts estimate the country had millions of cases every year, so many that the vast majority were never reported. Each year about 500 people died, and many suffered lifelong impacts, such as breathing problems. Vaccination quickly led to a decline in cases and deaths, and in 2000 the disease was declared eliminated.

Less than halfway through the year, 2019 has had the greatest number of cases since 1994.

A major outbreak from 1989 to 1991 caused more than 50,000 cases.

More than 10 percent of the people with measles this year, however, had been vaccinated. If people are vaccinated but exposed to measles, they may still become infected.

Breakdown of 2019 cases

Two overlapping groups have suffered the most this year: children under age 4 and people who were unvaccinated.

The first of the two-dose vaccination is often given to children around 12 months old. One dose of the vaccine is 93 percent effective, according to the CDC, and two doses are 97 percent effective in preventing infection. That still means that some people will not be protected.

Where parents don’t have to immunize their children

Parents in 17 states can opt out of vaccinating their children if they cite personal or philosophical objections. All states have medical exemption laws since some people cannot be vaccinated because of health issues, such as weakened immune systems. Almost all states grant religious exemptions for people who have religious beliefs against immunization.