NEW YORK (CBSNewYork) — There are growing concerns over the Delta variant.

It is spreading rapidly across the United States, and locally the highly contagious strain makes up the majority of new COVID-19 cases.

READ MORE: Mayor De Blasio Doubles Down On Municipal Workers Vaccine Mandate: 'We Have Contingency Plans In Place'

On Monday, the American Academy of Pediatrics recommended everyone over the age of 2 be masked up this upcoming school year, and the Centers for Disease Control issued a travel warning for the United Kingdom, saying even fully vaccinated travelers could be at risk for getting and spreading the variant.

It’s even spooking investors, with stocks tumbling Monday amid fears this could threaten the U.S. economic recovery, CBS2’s Vanessa Murdock reported.

In New York City, at least one City Council member is calling for an indoor mask mandate, but Mayor Bill de Blasio says vaccines are the best way.

“Vaccination is the reason we are in a very, very different situation than other parts of the country that are suffering,” de Blasio said.

Mark Treyger, the chair of the City Council’s Committee on Education, is making it clear where he stands on school plans. On Twitter, he wrote, in part, “DOE should offer a fall remote option for kids not of vaccination age,” adding, “I support 5 days a week in person instruction for all, but we need to follow science and adjust accordingly …”

De Blasio said New Yorkers have stepped up: 4.5 million fully vaccinated. That’s 53.5% of the population.

Watch: Mayor Bill de Blasio Discusses Mask Mandate, Vaccinations And More

That includes Marcie Goldberg, who believes New York handled its COVID response better than anywhere else in the country.

“I have very little fear of walking around the Upper West Side or anywhere in Manhattan,” Goldberg said.

Sabila Khan’s father died from COVID last April, before the vaccine was available. She told CBS2’s Jessica Layton she wishes more people would take this new spike seriously.

“I think if people knew how horrible it is for the person who is gasping for breath, literally. If they understood what that was like, I think they would be taking more precautions,” Khan said.

Khan, from Jersey City, is vaccinated, but often still wears her mask in public, especially indoors.

“Our children are still unvaccinated,” she said.

“Over 98% people who have been hospitalized or died as a result of COVID-19 this year in New York City are not fully vaccinated. So the choice is clear,” Health Commissioner Dr. David Chokshi said.

Even more so now than before, said Chokshi, as the Delta variant stands responsible for 69% of current city COVID cases.

“It is actually a more dangerous time right now to be unvaccinated given how contagious the Delta variant is,” Chokshi said.

News of the variant is what motivated Upper West Side resident CJ Claffey to sign up for the vaccine.

READ MORE: FDA Grants Emergency Use Authorization For Moderna And Johnson & Johnson's COVID Vaccine Booster Shots

“I am getting mine this week,” Claffey said.

He said it’s time to protect himself and those he cares about.

Cases are on the rise in the city: The daily case count average is 516. The positivity rate 1.69%, with hospitalizations at 0.35 per 100,000 cases.

“They’ve actually tripled in the last two weeks, over 500 new cases a day. At the same time, New Yorkers are wearing masks less,” said City Councilmember Mark Levine, who chairs the Health Committee.

Levine emphasized the need to do something now to blunt another wave.

“You are pushing for a re-instatement of the mask mandate?” Murdock asked.

“Yes. At a minimum, a recommendation guidance from public health authorities,” Levine said.

Levine said he believes a mandate would inspire solidarity amongst New Yorkers. Murdock asked New Yorkers their task on such a proposal.

“I think it’s up to the people,” Claffey said.

“I don’t think so,” Goldberg said.

COVID VACCINE

“It’s difficult to know if people are vaccinated or not, so I would say, yes, let’s wear the mask,” said Flavie Bagnol.

When asked about the possibility of reinstating the mask mandate to address the rise in cases, the mayor’s response was swift and firm.

“Simple answer: No,” de Blasio said. “Masks are not going at the root of the problem, vaccination is.”

New Jersey Gov. Phil Murphy boasted the vaccine is 99.92% effective.

“For your family, for your community, for public health, for common sense, for your own health, please go get vaccinated,” Murphy said.

“If you are vaccinated, you are safer, period. If you are not vaccinated, you are vulnerable,” de Blasio said.

Chokshi said the mask mandate remains in effect on public transit, schools and other high risk settings, like health care facilities.

MORE NEWS: Mayor De Blasio Announces Vaccine Mandate For All New York City Municipal Workers, Including First Responders

CBS2’s Jessica Layton contributed to this report. Editor’s note: This story was first published on Monday, July 19.

Vanessa Murdock