Blood-clotting issues linked to the Johnson & Johnson (J&J) COVID-19 vaccine are extremely rare, the head of the National Institutes of Health (NIH) said on Sunday as he pushed back against calls for the one-dose vaccine to be paused for women under the age of 50. NIH director Francis Collins made the remarks in response to advice from physician and CNN medical analyst Leana Wen, who said in a Washington Post op-ed that “the default position should be against administering the Johnson & Johnson vaccine to women under 50.” Wen’s piece was published after the Centers for Disease Control and Prevention’s (CDC) vaccine advisory committee voted to lift the pause on the J&J vaccine with no restrictions. In an emergency meeting Friday, members of the Advisory Committee on Immunization Practices (ACIP) said that they recommend resuming the use of the J&J vaccines in persons age 18 and older after a …