As measles cases continue to spread in many parts of the United States, Maine health officials on Friday announced that the state has recorded its highest ever immunization rate for its K-12 students.

The rate of coverage is “more than 97%” for the 2024-25 school year, breaking last year’s record of “more than 95%” immunized for common infectious diseases such as measles, chicken pox, polio and pertussis.

When coverage exceeds 95% scientists say a population has reached “herd immunity,” which means diseases are far less likely to spread because almost everyone is vaccinated or has been previously exposed to the disease. Herd immunity protects children who are unvaccinated, either because they are immune compromised and their doctor says they can’t receive vaccines, or are too young to get their shots.

Maine has not recorded a case of measles this year, and has not had a confirmed case since 2019. But cases across the country are continuing to spread, and 34 states have now reported measles cases. In New England, Vermont and Rhode island have reported cases. The U.S. Centers for Disease Control and Prevention is reporting 1,168 measles cases in 2025, and three deaths. Measles is highly contagious and can lead to pneumonia, hospitalizations, encephalitis and other long-term complications.

Maine used to have high opt-out rates for vaccinations, but a law that went into effect in 2021-22 eliminated religious and philosophic vaccination exemptions that allowed unvaccinated children to attend school. Medical exemptions are still permitted.

Since the law went into effect, vaccination coverage has improved and opt-outs have plummeted from 4.5% in 2020-21 to 0.8% in 2024-25. In some years before the law was implemented, opt-outs reached as high as over 6% and schools were more often reporting outbreaks of infectious diseases like pertussis and chicken pox.

Maine’s poor vaccination rates in the 2010s — spurred by disinformation about the safety of vaccines — led to an effort to pass a state law removing the religious and philosophic exemptions. Lawmakers approved the new exemption law in 2019 and it survived a people’s veto attempt by vaccine critics in a 2020 referendum vote.

Dr. Puthiery Va, Maine CDC director, said in a written statement Friday that “this achievement was possible because of the collective effort of our schools, families and communities, and we celebrate that.”

“Maine’s childhood vaccination rates are among the best in the nation, and the Maine CDC is proud to aid in building community-level protection,” Va said.