National Institutes of Health (NIH) Director Jay Bhattacharya will temporarily lead the Centers for Disease Control and Prevention (CDC) until President Trump names a permanent director. The CDC has not had a permanent leader since August 2025, when Health and Human Services (HHS) Secretary Robert F. Kennedy Jr. fired Susan Monarez. Deputy Health Secretary Jim O’Neill has been acting CDC director since then.

Bhattacharya gained his reputation during the COVID-19 pandemic as a vocal critic of the CDC’s response. Deeply opposed to lockdowns and highly skeptical of the effectiveness of masking, Bhattacharya, then a Stanford Medical School professor, took to writing and speaking out on social media. The CDC last month scaled back the recommended number of childhood vaccines, sparking alarm from pediatricians and public health experts who worry diseases that have been tamed by scientific advances may roar back with a vengeance.

Bhattacharya told Congress earlier this month that people should get vaccinated against measles, amid the largest outbreak in the U.S. in decades, and said he hasn’t seen evidence that vaccines cause autism, even as the president and Health and Human Services Secretary Robert F. Kennedy Jr. have added fuel to that theory. “I have not seen a study that suggests any single vaccine causes autism,” Bhattacharya told a Senate panel.

Bhattacharya gained notoriety for co-writing the Great Barrington Declaration, a petition signed by a group of scientists who advocated for younger individuals to live their normal lives and build natural immunity. Published in October 2020 and named after the Massachusetts town in which it was drafted, the declaration called for avoiding COVID-19 lockdowns and for a new pandemic plan that would protect the most vulnerable while allowing most people to resume normal activities, achieving herd immunity naturally.

The plan was criticized as “unethical” by Dr. Tedros Adhanom Ghebreyesus, director-general of the World Health Organization. Many public health experts voiced opposition, stating it could endanger lives. Bhattacharya continued to advocate against lockdowns, mask mandates, and COVID-19 vaccine passports throughout the pandemic before being tapped by HHS Secretary Robert F. Kennedy Jr. to lead the NIH. President Trump will nominate Jim O’Neill, who left HHS on Friday, to run the National Science Foundation.