In 1945, Sonia Klein walked out of Auschwitz. Every day of the 73 years since she has been haunted by the memory of what happened there, and the fate of the millions who never made it out of the Nazi death camps.

But Klein wonders, once she and the few survivors still alive are gone, who will be left to remember?

"We are not here forever," said Klein, now 92. "Most of us are up in years, and if we're not going to tell what happened, who will?"

Klein's worries are borne out by a comprehensive study of Holocaust awareness released Thursday, Holocaust Remembrance Day, which suggests that Americans are doing just the opposite.

Schoen Consulting, commissioned by The Conference on Jewish Material Claims Against Germany, conducted more than 1,350 interviews and found that 11 percent of U.S. adults and more than one-fifth of millennials either haven't heard of, or are not sure if they have heard of, the Holocaust.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

A group of Jews are escorted from the Warsaw Ghetto by German soldiers on April 19, 1943 in Poland. AP file

Of those who have heard of the Holocaust, many are fuzzy about the facts of a systematic campaign of murder that killed 12 million people, 6 million of them Jews. One-third of respondents — the number rises to 41 percent for millennials — think that two million or fewer people died.

"It's a must for people to remember," Klein said. The millions killed live through the survivors, she said, and "once we are gone they must not be forgotten."

With the youngest survivors now in their mid-70s, the chance of hearing first-hand stories is rapidly dwindling. Two-thirds of Americans do not personally know or know of a Holocaust survivor.

"We are painfully aware that this is the last generation of Holocaust survivors who can tell their stories," said Greg Schneider, executive vice president of the Conference on Jewish Material Claims Against Germany. "Transmitting those stories," Schneider continued, "becomes increasingly difficult in a world without survivors."

American citizens are not alone: Entire countries are changing the way they remember the Holocaust, known in Hebrew as the Shoah. The Polish government recently passed a bill making it illegal to blame Poland for any crimes committed during the Holocaust. More than half of the people exterminated by the Nazis were from Poland. Auschwitz, perhaps the best-known concentration camp and the death site of almost 1 million Jews, is in southern Poland, where it has been preserved as a memorial.

Schneider said there has also been an increase in anti-Semitism, and Americans agree, according to the survey. Sixty-eight percent of respondents believe there is anti-Semitism in the U.S. today. Separately, data released by the Anti-Defamation League shows a 57 percent spike in anti-Semitic incidents in the U.S. in the past year.

The way to fix this growing problem, Schneider said, is education. Only nine states mandate Holocaust curriculum in schools, and each state offers varying degrees of detail.

While one third of the annual 1.7 million visitors to the Holocaust Museum each year in Washington are American students, 80 percent of Americans say they have never visited a Holocaust museum.

"Unless you know what happened," Klein said, "you don't understand what never again means."