If states don't tighten vaccine exemption laws, the federal government may step in, U.S. Food and Drug Administration Commissioner Scott Gottlieb said.
"Some states are engaging in such wide exemptions that they're creating the opportunity for outbreaks on a scale that is going to have national implications," the FDA head said in an interview with CNN.
Gottlieb's comments come as some states are considering proposals that would change vaccine exemptions for personal or philosophical reasons. He first made the comments in an interview with Axios.
Gottlieb told CNN that "certain states" could "force the hand of the federal health agencies" if they don't make changes.
However, the FDA has not made any plans or announcements, and it's not certain the agency will.
In Washington state, lawmakers are considering two bills amid a measles outbreak that has infected at least 64 people in the state. One would ban personal or philosophical exemptions for the measles, mumps and rubella vaccine. A second bill would ban personal or philosophical exemptions for all vaccines required by schools and licensed day cares.
In Oregon, state Rep. Mitch Greenlick will propose a bill that would eliminate all nonmedical exemptions for vaccines, according to the Willamette Week. Greenlick's office did not return CNBC's request for comment.
On Tuesday, the Iowa state Senate rejected two bills related to vaccines. One would have allowed vaccine exemptions for philosophical reasons, and another would have stopped health-care providers and insurance companies from discriminating against people who refuse immunizations, the Associated Press reported.
Gottlieb called the Washington outbreak an "avoidable tragedy" on CNBC's "Squawk Box" in late January. "As vaccination rates decline, these kinds of epidemics are going to become more common," he said.
The outbreak in Washington prompted Gov. Jay Inslee to declare a state of emergency on Jan. 25.
Of the 64 cases in Washington since Jan. 1, 63 were in Clark County. The county's public health department reported that 55 of the 63 infected were not vaccinated against measles, six cases were unverified, and two cases had received one dose of the measles, mumps and rubella vaccine.
In Clark County, 45 of the 63 cases were children between the ages of 1 and 10 years old.
In 2018, 372 cases of measles were reported in the U.S., according to the Centers for Disease Control and Prevention. From Jan. 1 to Feb. 14, 2019, 127 cases of measles have been confirmed in 10 states, according to the CDC.
In 47 states, parents are exempted from vaccinating their children for religious reasons, according to the National Conference of State Legislatures. Seventeen states, including Washington, allow philosophical exemptions from vaccines.