In a first test of the Trump administration’s ability to respond to an infectious disease emergency, its top health official has shied away from one of the government’s most important tools, experts said on Sunday: loudly and directly encouraging parents to get their children vaccinated.

Robert F. Kennedy Jr., the health secretary, was widely criticized as minimizing the measles outbreak in West Texas at a cabinet meeting on Wednesday. In a social media post on Friday, he took a new tack, saying that the outbreak was a “top priority” for his department, Health and Human Services.

He noted various ways in which the department is aiding Texas, among them by funding the state’s immunization program and updating advice that doctors give children vitamin A.

But on neither occasion did Mr. Kennedy himself advise Americans to make sure their children got the shots. On Sunday night, he edged closer in an opinion piece for Fox News.

Mr. Kennedy acknowledged that vaccines “protect individual children from measles” and urged parents to talk with their doctors “to understand their options to get the MMR vaccine.”

“The decision to vaccinate is a personal one,” he added.

The Centers for Disease Control and Prevention, part of H.H.S., did not send its first substantive notice about the outbreak until Thursday, almost a month after the first cases in Texas were reported.