Jeanne M. Marrazzo, a University of Alabama at Birmingham infectious-disease expert, will succeed Anthony S. Fauci this fall as director of the National Institute of Allergy and Infectious Diseases, federal officials announced Wednesday.

The $6.3 billion research institute is among the largest of the 27 institutes and centers that constitute the National Institutes of Health, America’s flagship biomedical agency. NIAID is also particularly prominent given its involvement in the response to the coronavirus pandemic and other diseases; it has also received attention because of Fauci’s own high profile and Republicans’ ongoing efforts to investigate the institute’s workings.

Marrazzo is likely to face scrutiny as soon as she arrives in Washington, if not before, from lawmakers and watchdog groups that have taken aim at NIAID’s operations. Sen. Rand Paul (R-Ky.) and other Republicans have asserted that NIAID is too sprawling and have sought to split it into smaller institutes, an effort rebuffed by other lawmakers.

Fauci and other former top officials previously outlined challenges for new NIH leaders following the pandemic, such as what Fauci has called a growing “trend toward anti-science in the country.”

NIH has been without a confirmed director since longtime head Francis S. Collins stepped down in 2021. President Biden this year nominated Monica Bertagnolli, a cancer surgeon who runs the nation’s cancer institute, to lead the agency, but Sen. Bernie Sanders (I-Vt.) has yet to schedule a confirmation hearing for Bertagnolli, calling on the Biden administration to first do more to combat high drug prices. The NIAID job is not subject to Senate approval.

Marrazzo, an infectious-disease physician and epidemiologist who has been a principal investigator on NIH grants since 1997, has focused her research on the human microbiome and the prevention of HIV, as well as preventing infections in the female reproductive tract. She emerged as a frequent commentator during the pandemic, appearing on national television and urging Americans to get vaccinated and take other steps to protect themselves from the virus. An openly gay physician, Marrazzo has studied barriers to care for LGBTQ+ patients and advocated addressing them.

“Dr. Marrazzo brings a wealth of leadership experience from leading international clinical trials and translational research, managing a complex organizational budget that includes research funding and mentoring trainees in all stages of professional development,” Lawrence A. Tabak, NIH’s acting director, said in a statement.

Marrazzo did not immediately respond to a request for comment. An out-of-office message said she is away from email because she is working as an attending physician.

Advocates cheered her selection, noting that it came amid a rise of sexually transmitted infections across the United States, including a surge of syphilis cases among infants.

“Dr. Marrazzo has devoted her career to fighting sexually transmitted infections,” David C. Harvey, executive director of the National Coalition of STD Directors, said in a statement, adding that her selection ensures that those infections “will be taken seriously in the national policy environment.”

Fauci led the infectious-disease institute for 38 years as it played a key role responding to HIV/AIDS, the coronavirus and other infectious diseases, winning acclaim from public health experts — including his eventual successor.

“Great opportunity to thank Dr. Fauci today for his unparalleled commitment to advancing science & communication,” Marrazzo posted on social media in October 2022.

Fauci stepped down in December after serving as the face of the coronavirus response under Biden and at the pandemic’s outset under President Donald Trump, when he became the target of GOP-led political attacks. Hugh Auchincloss Jr., a longtime deputy of Fauci’s, has been serving as NIAID’s acting director.

Fauci, who said he did not have a close relationship with Marrazzo and was not involved in her selection, applauded the NIH search committee in an interview with The Washington Post.

“She’s an experienced infectious-disease person; she’s very well-liked,” Fauci said, citing her research into sexually transmitted diseases and noting that Marrazzo was a part of the clinical trials network he helped construct decades ago.

Fauci acknowledged the growing focus on NIH and his institute, warning that Marrazzo would probably face her own share of scrutiny.

“Sometimes, my sticking with data and facts generated a lot of antagonism on the part of people with extreme views,” Fauci said. “She will likely face that. … I believe she will be up to it as long as she stays anchored in science and evidence, and in keeping an open mind.”

Michael Saag, who has worked with Marrazzo for more than 20 years, said she has the leadership skills to oversee programs inside and outside of the institute, and the chops to handle potentially adversarial hearings on Capitol Hill and negative publicity that might come with the role.

“Unfortunately, in our current political environment, just having a position like this will be a lightning rod for a lot of hate speech and attack[s],” said Saag, a professor of medicine and infectious diseases at the University of Alabama at Birmingham. “She’s got a tough skin. I think she’ll be able to manage it well.”

Marrazzo has experience working with top state officials and others amid a crisis. During the height of the pandemic, she participated in weekly calls with Alabama officials and others to confront the latest challenges and navigate thorny issues, such as students returning safely to classrooms, Saag said.

Peter Staley, an HIV activist who sat on the NIH search committee that selected Marrazzo, praised her as one of the “amazing candidates” to fill Fauci’s role.

In social media posts, Staley urged Marrazzo to keep the institute focused on persistent challenges such as HIV and newer concerns such as long covid, and also address how the institute works with the private sector on drug development — a frequent point of contention between activists and the federal government.