Children and teenagers make up almost 60 percent of confirmed cases.

A total of 5,182 confirmed measles cases have been reported in the United States to date in 2026, according to data released by the Centers for Disease Control and Prevention (CDC).

The figure for the highly contagious but vaccine-preventable disease is the highest number reported by the CDC since 1991.

Children below the age of five make up 18 percent of cases, while children between ages five and 19 account for 41 percent of cases.

In total, children and teenagers account for about 59 percent of confirmed cases.

The majority of cases, a total of 4,993, were outbreak-associated.

The outbreak comes as vaccination coverage among US kindergarteners has decreased from 95.2 percent during the 2019-2020 school year to 92.4 percent in the 2025-2026 school year.

The number of confirmed cases by November 2026 is more than double the 2,289 confirmed measles cases reported in 2025.

Dispute over death toll

According to CDC data, four people have died due to measles in 2026.

However, the agency’s national death toll is lower than the number of measles-related deaths reported by state officials, particularly in Pennsylvania, the state hardest hit by the outbreak.

Pennsylvania’s Department of Health reported six deaths and 1,487 cases this year.

The federal count has been at the centre of a dispute between Pennsylvania Governor Josh Shapiro and US Health Secretary Robert F Kennedy Jr over how measles deaths are classified.

Pennsylvania reports “measles-associated” deaths after a person with confirmed measles dies within 30 days of developing symptoms, unless the death resulted from an unrelated event.

In August, Pennsylvania reported that two unvaccinated people died of measles. The CDC initially included the deaths in its national tally but subsequently removed them after Kennedy, a vaccine sceptic, questioned whether measles had caused or contributed to the fatalities.

The CDC has said it is working with the US Council of State and Territorial Epidemiologists to establish a standardised definition for measles deaths.

Infectious disease experts warn that the dispute over how to classify the deaths puts the CDC at odds with a longstanding approach to tracking the consequences of measles.

Epidemiologists have told Al Jazeera that tracking “measles-associated” deaths has long been a standard used by the World Health Organization and the CDC.

The US declared the virus eliminated more than two decades ago. Measles cases have also increased globally, particularly in communities that are vaccine-sceptical or where there are gaps in healthcare access.

Experts warn that declining vaccination rates in one geographic location can leave people thousands of miles away vulnerable, making measles prevention a shared global responsibility.