The announcement came as US president Joe Biden directed the US Labor Department to require all private businesses with more than 100 employees to ask for proof of vaccination or a negative Covid test.
Ms Williams said she understood that “vaccines have been essential in the effort to end this pandemic”, but that following advice from her family doctor, “taking the vaccine at this time is not in my best interest.”
“After a lot of prayer and deliberation, I have decided I must put my family and personal health first,” she wrote on Twitter.
“I will miss being on the sidelines and am thankful for the support of my ESPN family. I look forward to when I can return to the games and job that I love.”
Her decision comes in spite of advice from the US Centres for Disease Control and Prevention (CDC), which recommends people and their partners trying to get pregnant should get vaccinated.
“Currently no evidence shows that any vaccines, including COVID-19 vaccines, cause fertility problems (problems trying to get pregnant) in women or men,” the CDC says.
Ms Williams, who covers college sports and joined ESPN in 2011, added that her decision was “deeply difficult” and “not something I take lightly”.
Disney, which owns ESPN, has mandated that all employees be fully vaccinated before the end of September. The network employees around 4,000 people.
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