Friday afternoon, the USTA announced proof of at least one dose of a COVID-19 vaccine will be required for all ticketholders over the age of 12.
Initially, it was announced that the tournament would be back to full capacity with no requirements for masks, vaccines or a recent COVID test.
Those protocols are similar to those at New York's baseball stadiums, which have been at full capacity since June with no vaccine mandates.
"I've gotten vaccinated myself, and I know the majority of folks do get vaccinated, so I feel comfortable without wearing a mask and such," said Robert Hikel, of Cherry Hill, New Jersey.
The decision to host a massive tennis tournament with fans from all over the world and not require vaccines drew some criticism.
"This is alarming," New York City Councilman Mark Levine said.
Levine is chair of the City Council's health committee.
"And if there's no screening for vaccination, or even a negative test, this is an extremely high-risk event," he said.
CBS2's Dr. Max Gomez says outdoors is always safer when it comes to crowds, but he adds, "There is no such thing as zero risk when you're at an event with tens of thousands of fans, many not wearing masks and who may not be vaccinated. There's a chance, probably very small, that you could get infected with this coronavirus."
The USTA says they decided to change their policy after they learned the mayor's office would be mandating proof of vaccination for the entrance to Arthur Ashe Stadium.
"Given the continuing evolution of the Delta variant and in keeping with our intention to put the health and safety of our fans first, the USTA will extend the Mayor's requirement to all US Open ticket holders 12-years-old and older," the USTA said in a statement.
New York City requires vaccination for indoor dining, gyms and lots of other indoor activities.
On Aug. 3, Mayor Bill de Blasio called the vaccine "the key to the city."
"If you're vaccinated, all that's going to open up to you," he said. "But if you're unvaccinated, unfortunately, you will not be able to participate in many things."
The USTA says unvaccinated ticketholders can apply for a refund through their Ticketmaster account.
As the world's top tennis stars prepare for the U.S. Open, fans are ecstatic to be back in person.
"It's crazy. You can tell the difference in the energy of the players, too," Mineola resident Jai Menun said.
Fans were banned from the Open last year due to COVID.
CBS2's Nick Caloway contributed to this report. Editor's note: This story was published Aug. 27.
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