Washington (CNN) When first lady Melania Trump unveiled her "Be Best" platform last year, a key pillar of her signature initiative was promoting the "well-being" of children. But as a measles outbreak threatens the well-being of some US children , the first lady herself has yet to weigh in on vaccinations, thus far declining to speak out on a critical topic.

Celebrating one year of Be Best in the White House Rose Garden Tuesday, Trump highlighted her efforts promoting children's kindness, healthy living and respect, as well as a newly expanded focus on online safety and talking about the dangers of opioid abuse. National Institutes of Health director Dr. Francis Collins was invited to the podium to make brief remarks, and he emphatically said something the first lady didn't.

"To make an important and timely point, vaccines are a highly safe and effective line of defense against measles and other infectious diseases. So if you want your kids to Be Best, do what the President said last week: get them to get their shots," Collins said to applause. A spokesperson for the NIH declined to comment further.

The first lady's office did not respond to multiple requests for comment to this story. Her opinions on vaccinations remain unclear.

According to the US Centers for Disease Control and Prevention, 764 individual cases of measles have been confirmed in 23 states from January 1 to May 3 of this year, marking "the greatest number of cases reported in the US since 1994 and since measles was declared eliminated in 2000."

The highly contagious disease can spread among those who are unvaccinated, leaving the nation's infants, who generally the first of two doses of receive the measles vaccination when they are 12 months old, extremely vulnerable.

Health officials blame the rise of vaccine-preventable diseases, including measles, on an increase in anti-vaccine rhetoric.

The President speaks out

President Donald Trump publicly made multiple claims linking child vaccinations to autism before entering office, but he changed his tune last month amid news of the outbreak.

"They have to get the shots. The vaccinations are so important. This is really going around now. They have to get their shots," Trump told CNN's Joe Johns when asked his message to parents in late April.

Though multiple studies have found that there is no link between vaccines and autism, Trump had voiced skepticism toward child vaccinations over the past decade. It's unclear if the first lady shared or shares those views.

During a 2015 Republican primary presidential debate on CNN , Trump told CNN's Jake Tapper that he was in favor of "smaller doses (of vaccinations) over a longer period of time."

"Autism has become an epidemic. Twenty-five years ago, 35 years ago, you look at the statistics, not even close. It has gotten totally out of control. I am totally in favor of vaccines. But I want smaller doses over a longer period of time," Trump said at the time.

The power of the platform

First ladies in recent history have had an enormous power and opportunity to shine a light on a wide variety of issues through their platforms and appearances.

Kate Andersen Brower, a CNN contributor and author of "First Women: The Grace & Power of America's Modern First Ladies," said that those who have been most effective have used their platforms to address the health, both physical and emotional, of children.

"When they wade into weighty policy issues, as Hillary Clinton did, it always breaks bad for them. When Barbara Bush held a baby suffering from AIDS, it sent an extremely powerful message at a time when some people were worried about catching AIDS simply by touching someone who had it," Brower said.

"First ladies don't have to make a campaign of something, they just need to make sure the press is there to capture a moment. Barbara Bush knew how consequential that photo would become," she added.

Trump, Brower said, has the ability to make a similar impact with vaccinations and Be Best.

"Melania could voice her support for vaccinations and maybe even visit a doctor's office where children are being vaccinated. It's as simple as that," she said.

The outreach to Trump over vaccinations began long before the measles outbreak. Former first lady Rosalynn Carter, a longtime vaccination advocate who is the president and co-founder of the nonprofit organization Vaccinate Your Family, reportedly delivered a letter to Trump through aides on Inauguration Day requesting a meeting on vaccinations.

Vaccinate Your Family declined to comment to CNN on the matter.

Carter, 91, continues to use her platform as a former first lady to advocate for vaccinations.

"This crisis is not caused by an inability to access life-saving vaccines. Rather, families have been misled into believing that vaccines pose a greater risk than the diseases they prevent. This is simply untrue," she wrote in an April USA Today op-ed

She continued: "Families should understand that opting out places their loved ones and their community in grave danger... Get the facts: Vaccines are safe and effective, and they save lives."

The administration

JUST WATCHED Wife of Trump aide: Women in military should expect sexual harassment Replay More Videos ... MUST WATCH Wife of Trump aide: Women in military should expect sexual harassment 02:27

Vaccination skeptics have been associated with Trump's presidential campaign and his administration.

In 2018, a top Veterans Affairs Department appointee named Thayer Verschoor came under fire for spreading conspiracy theories. Among one of his social media posts, he shared a list of 35 reasons to vote for Trump, which included Trump "warning" America of the "dangers" of vaccines.

Darla Shine, the wife of former White House communications chief Bill Shine, has espoused anti-vaccine views for years . While Bill Shine was in the White House, Darla Shine called for bringing back childhood diseases, such as measles, which she claimed boosted immunity and "keep you healthy & fight cancer."

However, health officials within the administration in recent weeks have promoted vaccinations. Health and Human Services Secretary Alex Azar, CDC director Robert Redfield, and acting Food and Drug Administration commissioner Ned Sharpless all echoed Collins' Rose Garden message during National Infant Immunization Awareness Week.