Pennsylvania has recorded more than 1,000 measles cases this year, the largest state outbreak in over three decades, as infections continue to rise across the US.
The outbreak, which began in April west of Philadelphia, has reached 1,004 cases, including 198 hospitalisations and five deaths, state officials said Monday.
The US is witnessing its worst measles year since 1991, with nearly 3,900 cases and eight reported measles-associated deaths over the past two years.
Texas, Utah, South Carolina and Ohio have also reported major outbreaks. South Carolina recorded 997 cases, while Ohio has crossed 200.
New York, which has reported more than 100 cases, declared a disaster emergency and expanded vaccine and testing authority.
Health experts have linked the outbreaks to declining vaccination rates. The US eliminated domestic measles transmission in 2000, but coverage has fallen below the 95% level considered necessary to prevent outbreaks.
Measles can spread through coughing, sneezing, breathing and contaminated surfaces, and remain airborne for up to two hours. International health officials will assess in November whether the US and Mexico retain measles-free status.
Lancaster County Coroner Dr Stephen Diamantoni said six-week-old Mary Stoltzfus died from measles, while newborn Ivan Miller died from a ruptured spleen, with measles listed as a contributing condition.
Neither was old enough for vaccination. Governor Josh Shapiro said vaccination could have prevented the deaths, while Health Secretary Robert F Kennedy Jr questioned the reports.
The CDC later added two deaths to its dashboard, drawing transparency concerns from public-health experts.
