Protesters March in Washington Against Covid-19 Vaccine Mandates

The organizers said they would be protesting mandates, not vaccines themselves. “Since the vaccines do not stop people from getting sick, why should we impose them as a requirement to keep one’s job or to enjoy the freedoms that we have always enjoyed such as eating at a restaurant, going to a concert, or attending school or the university?” said Louisa Clary, an organizer, in an email.

Vaccines and booster shots offer superior protection from the Delta and Omicron variants of the Covid-19 virus, according to three new studies released by the Centers for Disease Control and Prevention.

In one of the studies published Friday, a CDC analysis found that a third dose of either the vaccine from

Pfizer Inc.

and

BioNTech SE

or

Moderna Inc.

was at least 90% effective against preventing hospitalization from Covid-19 during both the Delta and Omicron periods.

“Those who remain unvaccinated are at significantly higher risk for infection and severe Covid-19 disease,” CDC Director

Rochelle Walensky

said Friday. “Protection against infection and hospitalization with the Omicron variant is highest for those who are up to date with their vaccination, meaning those who are boosted when they are eligible,” Dr. Walensky said.

One of the speakers at Sunday’s march was Robert F. Kennedy Jr., who has criticized vaccines for years. During his remarks, Mr. Kennedy suggested people in the future won’t be able to escape surveillance, citing so-called vaccine passports, and suggested conditions would be worse than in Nazi Germany because he said some people could escape the Nazis.

The Auschwitz-Birkenau Memorial and Museum condemned his comments. “Exploiting of the tragedy of people who suffered, were humiliated, tortured & murdered by the totalitarian regime of Nazi Germany—including children like Anne Frank—in a debate about vaccines & limitations during global pandemic is a sad symptom of moral & intellectual decay,” the museum said on Twitter.

The Biden administration has proposed increasingly strict measures to try to boost the nation’s vaccination rate as variants of the coronavirus continue to cause infections and strain hospitals. Nearly 210 million people in the U.S. are fully vaccinated, roughly 63% of the U.S. population, according to the CDC.

The administration has attempted to impose mandates, though some of their plans have run into legal obstacles. On Friday, a federal judge blocked the Biden administration’s Covid-19 vaccine requirement for federal employees.

Also this month, the Supreme Court blocked the administration’s Covid-19 vaccine-or-testing rules for large private employers. The high court, however, allowed the administration to require vaccinations for healthcare workers whose facilities participate in Medicare and Medicaid.

Some state and local officials have ordered their own kinds of mandates. Earlier this month, Washington, D.C., began requiring people to show proof of Covid-19 vaccination to enter many indoor businesses.

Some two months since Omicron began its rapid spread around the world, areas of the U.S. hit early by the variant’s spread have started to see some relief. Still, hospitals in some states remain under significant strain, and infections have kept millions of people in the U.S. home sick or caring for someone with Covid-19 symptoms, while others say they are working despite illnesses.

Dr. Anthony Fauci,

President Biden’s chief medical adviser, said Sunday that most states could reach a peak of Omicron cases by mid-February. Speaking on ABC News’ “This Week with George Stephanopoulos,” Mr. Fauci said, “Even with Omicron, boosting makes a major, major difference in protecting you from hospitalization and severe outcomes.”

Write to Alexa Corse at alexa.corse@wsj.com