World No 1 Ashleigh Barty is among several players who have been given access to the COVID-19 vaccine through a WTA Tour initiative.
Barty and her Australian coach Craig Tyzzer were among those who took advantage of the WTA's offer at a tournament in South Carolina earlier this month.
The former French Open champion was speaking after she moved into the quarter-finals of the Porsche Tennis Grand Prix with a comfortable 6-0 7-5 win over Laura Siegemund in Stuttgart having been given a first-round bye.
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"We were looking at different avenues to try and get vaccinated without jumping the queue in Australia to see what our options were, and we weren't able to get much of an answer before we left in March," said Barty, who turns 25 on Saturday.
"We were able to get the vaccine, as were a lot of other players, through the Tour and that they had organised through a certain pharmacy that had extras, and that was important to me knowing that those who were the most vulnerable were able to get it first."
Barty spent the last year back home in Australia, mostly due to the pandemic, and the Miami Open was her first tournament abroad since February 2020.
"It was nice to know that we have got that small layer of protection," Barty said, adding that she had experienced a few side effects from the vaccine.
"We still do the right things and abide by all the rules and the guidelines set in place by the Tour but knowing that we had that little bit of extra protection puts us at ease a bit more."
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No 3 seed Sofia Kenin, though, is out after she lost to Anett Kontaveit of Estonia, who booked her quarter-final place with a 7-5 6-4 win.
Earlier, sixth seed Karolina Pliskova needed three sets to see off lucky loser Tamara Korpatsch, progressing 7-5 3-6 6-3 as she looks to emulate her 2018 title win.
Another former French Open champion Jelena Ostapenko defeated qualifier Stefanie Voegele 6-4 7-5 and will meet Pliskova in the second round.
Two-time former tournament winner Angelique Kerber cruised past Ekaterine Gorgodze, defeating the 11th seed 6-2 6-2.
Marketa Vondrousova beat fellow Czech player Marie Bouzkova 6-1 7-6 (8-6) to secure a second-round match against No 2 seed Simona Halep.
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