Pennsylvania’s measles outbreak has grown to 890 confirmed cases across 39 counties, after health officials reported 55 new infections in just two days.

The state Department of Health announced the update on Friday. The outbreak has led to 173 hospitalizations and four measles-associated deaths this year, officials said.

Fewer than 1 percent of reported cases occurred in people who had been vaccinated against measles, the department said. About 31 percent of cases are in residents under 18. Lancaster County remains the hardest-hit area, with 359 confirmed infections.

The outbreak began in late April. Since then, more than 5,300 MMR vaccine doses have been given through 165 pop-up clinics in affected communities, with more clinics planned.

The update came amid political controversy. Health Secretary Robert F. Kennedy Jr. questioned the state’s reported deaths on social media, suggesting they may have been fabricated. In August, the CDC’s newly appointed director ordered staff to leave two Pennsylvania measles deaths out of the national count while the agency reviewed additional information.