Doxy-PEP for STIs and HIV Vaccine Research: Dr. Dieffenbach’s First Update from CROI 2024

Content From: HIV.govPublished: March 05, 20243 min read


During the first full day of presentations at the 2024 Conference on Retroviruses and Opportunistic Infections (CROI), we spoke with NIH’s Dr. Carl Dieffenbach about some of the new HIV research presented about Doxy-PEP for STIs and HIV vaccines. Dr. Dieffenbach is the Director of the Division of AIDS at NIH’s National Institute of Allergy and Infectious Diseases. He spoke with Louis Shackelford of the HIV Vaccine Trials NetworkExit Disclaimer. Watch our conversationExit Disclaimer with Dr. Dieffenbach.

Insights from Doxy-PEP Use in Real World Settings


At last year’s CROI, researchers presented results from an NIH-supported study on using a preventive dose of the antibiotic doxycycline as post-exposure prophylaxis within 72 hours after condomless sex to prevent bacterial sexually transmitted infections (STIs), an approach that has become known as Doxy-PEP. (View Dr. Dieffenbach’s discussion of those findings.) Here at CROI 2024, Dr. Annie Luetkemeyer of the University of California, San Francisco, shared additional findings from the open-label extension of that original study, which found sustained reduction of bacterial STIs among men who have sex with men and transgender women living with HIV or on PrEP in Seattle and San Francisco. The San Francisco AIDS Foundation (SFAF) was one of the first organizations in the U.S. to roll out Doxy-PEP, beginning in late 2022 when it was offered to all active PrEP clients at their visits at the Magnet clinic. SFAF medical director Dr. Hyman Scott reported that there was high uptake among clients and that bacterial STIs decreased by nearly 60% in less than a year at SFAF’s clinicExit Disclaimer. The decline was highest for syphilis (78%) and chlamydia (67%). The San Francisco Department of Public Health (SFDPH) presented the first findings to measure the effect of Doxy-PEP at the population level. Their analysis, presented by epidemiologist Madeline Sankaran, showed a substantial and sustained decline in the number of chlamydia and early syphilis infections in San Francisco among men who have sex with men and transgender women over the 13 months after the Department released guidelines for the use of Doxy-PEP. As in the other studies presented, SFDPH did not see corresponding significant declines in gonorrhea. Doxy-PEP is not recommended for cis-gender women because there is not yet evidence to suggest it is effective for them.

HIV Vaccine Trials Continue

Dr. Dieffenbach also discussed ongoing research to find a vaccine to prevent HIV, the topic of several presentations at the conference so far. Since there are a number of Phase I HIV vaccine trials currently underway, he and Louis spoke about what those smaller trials do. Then they discussed what some of the HIV vaccine trials currently underway are exploring.

Other Studies of Interest Presented on Monday

Some of the other studies presented centered on broadly neutralizing antibodies (bNAbs), including bNAbs as part of HIV therapy and how different HIV variants can affect bNAb efficacy as a treatment method. A new analysis from the pivotal HVTN 083 study of long-acting PrEP with cabotegravir found no significant risk of hypertension in people using the method, which had been a concern in some previous clinical studies of the same class of antiretroviral drugs.

About CROI

CROI is an annual scientific meeting that brings together leading researchers and clinical investigators from around the world to present, discuss, and critique the latest studies that can help accelerate global progress in the response to HIV and AIDS and other infectious diseases, including STIs and viral hepatitis. More than 3,635 HIV and infectious disease researchers from 73 countries are gathered in Denver and virtually this year for the conference. More than 1,000 summaries of original research are being presented at CROI. Visit the conference websiteExit Disclaimer for more information. Abstracts, session webcasts, and e-posters will be published there for public access in 30 days.

More HIV Research Updates to Follow on will be sharing additional video interviews from CROI 2024 with NIH’s Dr. Carl Dieffenbach, CDC’s Dr. Jono Mermin and Dr. Robyn Neblett Fanfair, and others. You can find all of them on’s social media channels and recapped here on the blog.