Some of the world's best tennis players are congregating in New York for the US Open, the season's final grand slam.
They do so at a time when there appears to be a sense of vaccine hesitancy among some of the sport's leading stars.
Men's world No. 3 Stefanos Tsitsipas has been the latest high-profile star on tour to have voiced vaccine hesitancy.
Women's world No. 2 Aryna Sabalenka also expressed hesitancy towards inoculation against Covid-19 back in March, saying: "I don't really trust it. For sure, I don't want my family to take it. If I will have to do it, I will really think twice before I take it."
Sabalenka's representatives didn't respond to CNN's request for comment on whether her stance had changed ahead of the US Open, where players from the men's ATP Tour and the Women's Tennis Association (WTA) Tour will compete at the US Open.
In a statement sent to CNN, a spokesperson for the WTA said nearly 50% of its players are vaccinated, though it has set a target of 85% by the end of the year.
The spokesperson said the organization "believes in and encourages everyone to get a vaccine," but the decision to vaccinate was "a personal decision, and one which we respect."
The ATP Tour, the men's tennis organization, said its current vaccination rate is "just above 50%."
In a statement to CNN, a spokesperson said the tour "continues to strongly recommended vaccination to players, based first and foremost on scientific evidence supporting the health benefits and protection provided," but that the decision for each player to vaccinate remained one of "free choice."
MaliVai Washington, a Wimbledon finalist and four-time winner on the ATP Tour, says players are in a privileged position to be able to influence others when it comes to receiving the vaccine.
"When I look at the ATP and the WTA Tours, the elite international athletes, they can show a huge leadership role right now," Washington told CNN.
"When I say leaders, these athletes on the tour, they have a significant influence on many people who are following them and if they are an advocate for it, you know, people will say: 'You know what, I'm gonna take another look at this. I'm going to follow that. If so-and-so is doing it, maybe it's okay for me.'
"I think they could have a big impact on vaccination rates if, let's say, a handful of players on the men's and women's tours came out saying: 'Yeah, I just got vaccinated.'"
However, Washington, who says he is vaccinated, doesn't necessarily believe players have the responsibility to use their platforms to publicly advocate for others to get vaccinated.
Rather, he believes they share the same responsibility as the general public to do it to protect themselves and those around them.
"Every individual is going to look at the word 'responsibility' differently," he explains. "I personally think it is everyone's responsibility to get the vaccine ... now, not everyone feels comfortable promoting it and getting out there and talking about it and getting the vaccine on camera because they don't feel that it's their responsibility.
"If I were on the tour today, I would have no problem publicly announcing that I am taking the vaccine and I would probably encourage other people to do the same.
Earlier this year, 20-time grand slam champion Roger Federer revealed he has been vaccinated, while long-time rival Rafael Nadal has also publicly supported vaccinations.
Last week on CNN, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, outlined a 2022 timeline for when "we'll start to get some good control" over Covid-19 in the US -- if vaccinations pick up.
"I mean it's really how many people get vaccinated, how many people step up and say, 'You know, we've had enough of this, we've got to put an end to this terrible outbreak that's completely disrupted our lives,'" Dr. Fauci later told CBS This Morning on Tuesday.
Except the message espoused by Fauci and other leading public health experts across the world appears to be unpersuasive for many elite tennis players.
Tsitsipas' recent comments were enough to draw a rebuttal from the Greek government, with spokesman Giannis Oikonomou saying the 23-year-old "does not have the knowledge and studies to assess the need for vaccinations."
Ahead of the start of the US Open, Tsitsipas' agent didn't respond to CNN's question as to whether he had been vaccinated following Oikonomou's comments.
In a statement sent to CNN, a spokesperson for the ITF, the governing body of world tennis, said: "The ITF continues to update the protocols that all ITF-sanctioned tournaments and participants must follow in order to mitigate the risk of exposure to, and spread of, Covid-19.
"While it remains a personal decision for each individual, we would strongly encourage all participants in ITF events to take up the Covid-19 vaccination as it becomes available to them in order to further protect themselves and others.
"It is in everyone's interests that restrictions can be responsibly eased for the benefit of participants, tournament hosts and the wider community."
US Open rules
But as hundreds of tennis players jet in from all around the world, there are potential real-life consequences for New Yorkers, not least the individuals working behind the scenes at the US Open.
On Saturday, the United States Tennis Association (USTA) announced that the New York City Mayor's office will be mandating proof of COVID-19 vaccination from spectators for entrance to much of the US Open, which had previously not been the case.
"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 statement read.
"Any US Open attendee with tickets to Arthur Ashe Stadium, Louis Armstrong Stadium, The Grandstand, or the grounds of the US Open, will be required to provide proof of at least one dose of a COVID-19 vaccine to enter the grounds of the USTA Billie Jean King National Tennis Center."
US Open regulations state that guests attending the tournament, like the players, will also require proof of vaccination for indoor dining areas due to New York City's recent executive order.
Players will also have to show proof of vaccination to eat at restaurants at the US Open's Flushing Meadows venue -- and everywhere else in New York City -- but the city's vaccination mandates for indoor events will not apply to events ancillary to the tournament, such as press conferences, unless they are residents of the city.
US Open rules require players to take a Covid test on arrival, but they will not have to self-isolate while awaiting the result.
In a statement sent to CNN, an ATP spokesperson said: "Vaccination also helps players reduce the risk of being ruled out from competition, by virtue of being a positive case or a close contact.
"We regularly reinforce this position in our communication to players, which has included several virtual sessions with medical experts on the subject in recent months."
US Open director Stacey Allaster last week cited New York City's vaccination rate of almost 70% as one reason organizers stand behind their tournament protocols.
Fans filling the stands at Flushing Meadows will be a stark contrast to the 2020 edition of the tournament, which was played entirely behind closed doors and even required players to stay largely within a US Open "bubble."
One leading tennis player has already had to withdraw from the upcoming US Open after testing positive for Covid-19.
American Sofia Kenin, the 2020 Australian Open champion and currently ranked fifth in the world, said on social media she is vaccinated and her symptoms are "fairly mild."
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