WASHINGTON — Most states are not prepared to handle outbreaks of severe infectious diseases, according to a new report by the Trust for America’s Health and the Robert Wood Johnson Foundation.

“Outbreaks: Protecting Americans from Infectious Diseases” found that half the states and the District of Columbia scored five or lower out of a possible 10 on measures related to the prevention, diagnosis, detection and response to disease outbreaks.

Maryland, Massachusetts, Tennessee, Vermont and Virginia led all states, each scoring eight out of 10.

California, Delaware, Nebraska, New Hampshire, North Dakota, Pennsylvania and Wisconsin were next, scoring seven out of 10.

Maine scored four out of 10.

Arkansas had the nation’s lowest score with two.

The recent Ebola cases in Dallas were a reminder “that we cannot afford to let our guard down” in preparing for major outbreaks, said Jeffrey Levi, executive director of the trust, a nonprofit health advocacy organization dedicated to disease prevention.

“Over the last decade, we have seen dramatic improvements in state and local capacity to respond to outbreaks and emergencies,” Levi said. “But we also saw during the recent Ebola outbreak that some of the most basic infectious disease control policies failed when tested.”

The report found that a majority of adults, 35 percent of seniors and more than 2 million preschoolers didn’t have all their recommended vaccinations. And only 14 states vaccinated 50 percent of their residents against the flu last year.

Only 16 states performed better than the national average for health care-related bloodstream infections. And only 10 cut the number of these infections between 2011 and 2012.

The report concluded that it was time to modernize the nation’s health system to deal with current and emerging disease threats.