Pennsylvania reports first U.S. measles deaths this year as outbreak grows
XLV•Vaccination rates and herd immunity
Vaccination rates of 95% or higher can prevent outbreaks by creating what is known as herd immunity that protects people unable to be vaccinated.
Two doses of the Measles-Mumps-Rubella shot provide 97% protection against the virus. Children typically first receive the vaccine when they are 12 to 15 months old and again at age 4 to 6 years of age.
According to Pennsylvania Department of Health data for the 2025-2026 school year, 93.2% of Pennsylvania kindergarten-age children had received the required two doses of MMR vaccine, down from 93.7% during the 2024-2025 school year.
In Lancaster County, 87.6% of kindergarten students received the required two MMR doses during the 2025-2026 school year.
"Because measles was largely eliminated in the Commonwealth for more than three decades, people are not familiar with this disease and don't fully understand the potential severity of the illness," said Pennsylvania Secretary of Health Debra Bogen.
