Measles cases have surged across Pennsylvania and neighbouring Maryland, while New York City and Washington DC have reported only single-digit totals, underscoring the sharply localised nature of the United States outbreak.
The Centers for Disease Control and Prevention recorded 3,471 confirmed cases across 47 US jurisdictions by September 17, 2026 — well above the 2,289 cases reported during the whole of 2025 and the highest annual total in 35 years.
Almost 95 per cent of this year’s cases were among people who were unvaccinated or whose vaccination status was unknown. The CDC said 39 new outbreaks had been reported in 2026, with 95 per cent of confirmed cases linked to an outbreak.
Pennsylvania measles outbreak
Pennsylvania has become the country’s principal north-eastern hotspot, with at least 767 confirmed cases reported across 38 counties and four measles-associated deaths.
The Pennsylvania Department of Health said two further deaths were confirmed on September 15, in Jefferson and Mifflin counties. Both people were unvaccinated, according to the department, which also reported 141 hospitalisations during the outbreak.
Philadelphia health officials have issued warnings over possible exposure at the Children’s Hospital of Philadelphia and Philadelphia International Airport. The airport exposure occurred in Terminals B and F, as well as connecting areas, between the evening of September 13 and the early hours of September 14.
The Philadelphia Department of Public Health said the airport case was separate from the exposures at the hospital. It urged anyone who may have been exposed to check their vaccination status and contact a healthcare provider if symptoms developed.
Maryland has recorded 41 confirmed cases as of September 17, with infections concentrated in St Mary’s, Cecil and Carroll counties. The state health department said there was no evidence of widespread community transmission, with many cases linked to household contacts.
New York and Washington avoid wider spread
New York City has reported six confirmed cases this year, according to the city’s health department, while Washington DC has recorded one case, identified in April.
DC Health issued an alert on September 14 warning medical providers about the rise in regional cases. Doctors were advised to screen patients with fever and rash carefully and to isolate suspected infections promptly.
Health officials say the difference between Pennsylvania’s large outbreak and the much lower totals in New York City and Washington reflects variations in local immunity and the presence of under-vaccinated communities.
Measles is airborne and can remain infectious in the air or on surfaces for up to two hours after an infected person has left an area. An imported case can therefore spread quickly when it reaches a community where vaccination levels are lower.
The CDC says roughly 95 per cent vaccination coverage is needed to maintain strong community protection. National coverage among US kindergarten children fell to 92.4 per cent during the 2025-26 school year, leaving an estimated 280,000 children vulnerable.
Infants under 12 months, pregnant women who are not immune and people with weakened immune systems are among those at greatest risk of serious illness. Health departments continue to advise people to check their MMR vaccination records and to call ahead before visiting a medical facility if they develop symptoms after a possible exposure.
