Sexually transmitted infections (STIs) are caused by bacteria, viruses, or parasites. STIs have a devastating impact on adults and infants and annually affect millions of people in the United States. Certain STIs can increase a person’s risk of developing cancer and increase the likelihood of acquiring or transmitting HIV. In addition, STIs can cause long-term health complications, especially in the reproductive and central nervous systems. In rare cases, they can lead to serious illness or death. 

NIAID supports research across the spectrum from basic to clinical science to develop effective diagnostic, preventive and therapeutic approaches to STIs in alignment with the National STI Strategic Plan. In recognition of National STI Awareness Week, NIAID shares a snapshot of new projects and recent scientific advances in STI research. 

Improving treatment for syphilis and trichomoniasis

New reports of syphilis and congenital syphilis are increasing at an alarming rate in the United States. Syphilis is caused by the bacterium Treponema pallidum. Benzathine penicillin G (BPG) is one of only a few antibiotics known to effectively treat syphilis. There is currently a shortage of BPG, and some people are allergic to penicillin antibiotics. In February 2024, NIAID convened a workshop with a wide range of experts on alternative therapies to BPG for the treatment of adult syphilis, neurosyphilis, and syphilis in pregnant persons and infants. The workshop addressed preclinical evaluation of candidate drugs, the potential need for studies on how candidate drugs are processed in the body during pregnancy, and how to approach clinical trials of treatment for congenital syphilis. This work is part of NIAID’s comprehensive portfolio of syphilis diagnosis, prevention, and treatment research. 

Trichomoniasis is the most common parasitic STI, caused by Trichomonas vaginalis. Trichomoniasis can increase the risk of getting or spreading other STIs, including HIV. The parasite can also cause inflammation of the cervix and the urethra. T. vaginalis is treated with an antibiotic drug class called nitroimidazoles. The currently recommended nitroimidazole, called metronidazole, cures 84-98% of T. vaginalis cases but does have high rates of breakthrough infection. A new project led by Tulane University will examine a single dose of secnidazole, a medicine in the same drug class, as a more effective and cost-effective treatment option for women and men. 

Developing a vaccine for herpes simplex virus 2

Herpes simplex virus 2 (HSV-2) is a common subtype of herpes simplex virus that is transmitted through sexual contact. The Centers for Disease Control and Prevention estimates that 18.6 million people aged 15 years and older United States live with HSV-2. In severe cases, HSV-2 may lead to life-threatening or long-term complications. There is no licensed preventive HSV-2 vaccine, and there is no cure. A new project led by the University of Pennsylvania seeks to define correlates of protection for HSV-2, meaning they intend to identify immune processes involved in preventing HSV-2 disease. They will do this by analyzing laboratory samples from animal studies of a promising preventive vaccine candidate that they developed with prior funding. That vaccine candidate is also now in an industry-sponsored early-stage clinical trial. The same project will expand on the HSV-2 targets in the preventive vaccine to develop a therapeutic vaccine concept to reduce recurrent outbreaks. This research responds to the scientific priorities in the NIH Strategic Plan for Herpes Simplex Virus Research.

Increasing fundamental knowledge of bacterial vaginosis 

Bacterial vaginosis (BV) results from an imbalance in the vaginal microbiome. BV can be caused by sexual activity, douches and menstrual products. BV can increase women’s biological susceptibility to HIV and other STIs and can cause premature birth or low birthweight if untreated in pregnant people. In a recent publication, NIAID-supported researchers, led by researchers at the University of Washington and University of California San Diego, shared findings on how damage to the vaginal skin barrier occurs during bacterial vaginosis. Those skin barrier cells, called epithelial cells, are covered in carbohydrate molecules called glycans. The research team found that people with BV had damaged glycans on their vaginal epithelial cells. They suggested that future work should examine the relationship between treatment and restoration of normal glycans. If an association is detected, it could help healthcare providers monitor for successful treatment outcomes to reduce the likelihood that BV will return after a course of treatment. The findings were published in Science Translational Medicine. 

These activities are among the research investments in NIAID’s STI portfolio. For more information on STIs, please visit:

• NIAID Diseases & Conditions: Sexually Transmitted Infections
• U.S. Department of Health and Human Services STI National Strategic Plan

NIAID-developed Vaccines May Provide Flexibility and Choice Among Ebola Vaccines

Ebola viruses cause devastating disease in people, resulting in severe and often fatal hemorrhagic fever called Ebola virus disease. Of the four species of Ebola viruses that cause disease in people, Zaire ebolavirus (EBOV) and Sudan ebolavirus (SUDV) have caused more than 30 known outbreaks in the last century, killing more than half of those with the disease. Scientists at NIAID’s Vaccine Research Center (VRC) developed novel vaccines to combat these viruses, which were advanced to clinical trials in response to the 2014-2016 Ebola epidemic in the West African countries of Guinea, Liberia, and Sierra Leone. In two phase 1/1b trials conducted in the United States and Uganda, the researchers evaluated combinations of the experimental vaccines against Ebola disease in healthy adults, finding them safe, tolerable, and capable of producing immune responses. Comparisons between the different vaccine regimens revealed important data on how the vaccines could be administered in routine and outbreak settings. The results of the trials were published last week in npj Vaccines.

In a Springer Nature Research Communities blog post published after the research article, the authors discussed how the vaccines were rapidly brought to clinical trials amid reports that cases of Ebola virus disease were spreading in Guinea in March 2014. At the time, there were no approved vaccines or therapeutics for Ebola virus disease. When outbreaks occur, Ebola virus spreads quickly, and severe symptoms and death can occur within weeks of infection. The rapid progression of Ebola virus disease in individuals often causes outbreaks to be short but deadly, although the threat of larger epidemics looms large. In 2014, the Ebola outbreak spread to Liberia and Sierra Leone, with a small number of travel-related cases in the U.S. and several African and European countries. Public health officials around the world feared the outbreak could become a global pandemic. 

At the same time, researchers at the VRC were preparing to bring new investigational Ebola vaccines, called cAd3-EBO, cAd3-EBOZ, and MVA-EbolaZ, to clinical trials. The scientists and their collaborators worked hard to accelerate the process and launch a clinical trial in the U.S. to test whether a two-dose vaccine regimen could be used in the event of a prolonged outbreak. The researchers also launched a similar clinical trial in Uganda. The two trials enrolled 230 healthy people, 174 of whom had already received an Ebola vaccine in previous studies. 

The trials evaluated “prime-boost” vaccine regimens, which first use a “prime” vaccine followed by a different “boost” vaccine. Each of the vaccines uses a portion of a protein from the surface of Ebola viruses called Ebola glycoprotein (GP) as the immunogen—the part of the vaccine that trains the body to generate an immune response without causing disease. The prime vaccines used in the trial were cAd3-EBOZ and cAd3-EBO, which use a vaccine vector based on a chimpanzee adenovirus not capable of replicating inside the human body, called cAd3. The cAd3 vaccines included either EBOV GP (the cAd3-EBOZ vaccine) or a combination of EBOV and SUDV GPs (the cAd3-EBO vaccine). The boost vaccine was MVA-EbolaZ, which uses EBOV GP with a different vector, modified vaccinia virus Ankara (MVA). Preclinical studies had shown the combination of vaccines could produce strong, protective immunity against Ebola virus disease in animals. 

Combining the results of the U.S. and Uganda trials, the researchers found the vaccines to be safe and tolerable in people with and without prior Ebola vaccinations. Additionally, the cAd3 Ebola vaccines produced immune responses in people, stimulating the production of antibodies against Ebola that reach high levels as soon as two weeks after vaccination and lasting up to 48 weeks after the prime and boost vaccinations. The researchers also found that different time intervals between the prime and boost vaccinations influenced the magnitude of antibody and cellular immune responses.

The 2014 Ebola outbreak was larger than any previously reported. When it was declared over in 2016, the disease had claimed 11,325 lives among the 28,652 reported cases. Several clinical trials evaluating Ebola vaccines, including cAd3 vaccines, were launched at the time, providing much-needed countermeasures against this deadly disease. Since then, new vaccines against Ebola virus disease have emerged, with one approved for use in the U.S., the European Union (EU), and several African countries, and a prime-boost regimen that was authorized for use in the EU.  

Given the unpredictable nature of Ebola outbreaks, several different vaccination strategies could be useful. These include routine vaccinations in regions where Ebola virus disease is known to occur, pre-exposure vaccinations of frontline workers during outbreaks, emergency vaccinations of people in outbreak zones, as well as the availability of multiple vaccines for different individuals. According to the researchers, these findings demonstrate that the cAd3 and MVA Ebola vaccines could make useful additions to countermeasures against Ebola virus disease, allowing for choice and flexibility among the currently available vaccines. Additionally, they note that the findings will inform the development of vaccine campaigns and emergency response strategies during Ebola outbreaks. 

References: 

M Happe, AR Hofstetter, et al. “Heterologous cAd3-Ebola and MVA-EbolaZ vaccines are safe and immunogenic in US and Uganda phase 1/1b trials.” npj Vaccines DOI: 10.1038/s41541-024-00833-z (2024).

AR Hofstetter, M Happe, et al. “Clinical Testing of the cAd3-Ebola and MVA-EbolaZ vaccines.” Springer Nature Research Communities (2024).

This blog is adapted and cross-posted from HIV.gov. 

On the final day of the 2024 Conference on Retroviruses and Opportunistic Infections (CROI), HIV.gov spoke with Deborah Persaud, M.D., professor of Pediatrics at the Johns Hopkins University School of Medicine and director of the Division of Pediatric Infectious Diseases at Johns Hopkins Children's Center, who reported findings from a study about whether very early initiation of antiretroviral therapy (ART) may limit the establishment of HIV reservoirs in newborns, potentially enabling ART-free remission. Dr. Persaud spoke with Catey Laube of NIAID’s Office of Communications and Government Relations. Watch their conversation below:

Four Children Achieve ART-free HIV Remission

The study Dr. Persaud presented at CROI began 10 years ago. HIV.gov spoke to Dr. Persaud at CROI 2013 when she presented the case of an infant born with HIV in Mississippi who initiated treatment at 30 hours of life, was taken off their ART at 18 months of age and remained in remission with no evidence of detectable HIV for 27 months. This was an uncommon finding because, typically, an interruption in treatment will lead to rapid resumption of HIV replication and detectable virus in the blood within weeks. Dr. Persaud and colleagues then began the NIH-supported study she reported on at CROI this year to carefully replicate that result in a research setting to determine whether the ART-free remission the “Mississippi baby” experienced was due to the very early start of HIV treatment within hours after birth and could be effective in other children.

Dr. Persaud reported on the experience of six children, all aged 5 years, who met multiple criteria to be eligible for a closely monitored ART interruption and whose parents consented. Four of the six children experienced HIV remission, defined as the absence of evidence of replicating virus for at least 48 weeks off ART. One of them had detectable HIV after 80 weeks. Two children did not experience remission, and their HIV became detectable within a few weeks after ART interruption. Children whose HIV became detectable resumed ART. The other three remain in remission. These promising findings will be followed by additional research to better understand the biological process that enabled the children to experience HIV remission off ART and to study early ART with newer drug regimens than were used in this initial study. Dr. Persaud cautioned that much more evidence is needed before this approach could be possible outside of the strictly monitored research setting. Read the study abstract. Read NIAID’s summary of the study findings.

Other Studies of Interest Presented on Wednesday

Some of the other NIH-supported research presented at CROI included a study that identified sex-based differences in latent HIV reservoirs, highlighting unique aspects of reservoirs in women. The findings point to the importance of including cisgender women in HIV cure studies. Read the study abstract. Another showed that a novel hepatitis B vaccine achieved up to 99% protection in people with HIV who had previously not responded to conventional hepatitis B vaccines. Read the study abstract.

Catch Up on More HIV Research Updates

HIV.gov has shared other interviews from CROI 2024 with federal HIV leaders, participating researchers, and community members. You can find all of them on HIV.gov’s social media channels and recapped here on the blog this week and next week.

This blog is adapted and cross-posted from HIV.gov. 

During the first full day of presentations at the 2024 Conference on Retroviruses and Opportunistic Infections (CROI), HIV.gov spoke with Carl Dieffenbach, Ph.D., director of NIAID’s Division of AIDS, about research presented on Doxy-PEP for sexually transmitted infections (STIs) and HIV vaccines. He spoke with Louis Shackelford of the HIV Vaccine Trials Network. Watch their conversation.

Louis also spoke with LaRon Nelson, Ph.D., R.N., F.N.P., F.N.A.P., F.N.Y.A.M., F.A.A., about community-engaged research, HIV prevention at CROI, and a new study (HPTN 096) he is leading to reduce HIV rates among Black men who have sex with men (inclusive of cisgender and transgender men) in the southern United States. Dr. Nelson is a professor and the associate dean at the Yale School of Nursing. Watch their conversation.

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 STIs, an approach that has become known as Doxy-PEP. (View last year’s Doxy-PEP discussion with Dr. Dieffenbach.) 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 United States 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 clinic. 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.

Community-Engaged Research

The importance and significant benefits of involving community in all aspects of HIV research was the first topic Dr. Nelson and Louis discussed. “If we don’t have community voices or engaged communities, we aren’t going to be asking the right questions or designing the studies in the best ways that will produce the outcome that we need, and we won’t end up with answers that are as relevant as they could be,” Dr. Nelson observed. He pointed to the dapivirine vaginal ring as an example of better outcomes because communities were involved in research. He said he hopes that community engagement in research continues to become more and more common, but it requires that researchers be willing to listen and, when needed, change their plans based on what they hear from community.

HIV Prevention Research at CROI

Dr. Nelson highlighted some of the HIV prevention topics at CROI that have caught his attention, such as increasing equitable use of long-acting injectable forms of HIV PrEP and treatment among different populations and in different countries. Other discussions of interest have included early studies on potentially very long-acting forms of HIV PrEP and exploration of possible dual prevention tools that would provide users with both HIV PrEP and contraception.

HPTN 096 Study

Finally, Dr. Nelson discussed an example of community-informed research that will soon be underway: the NIH-supported study through the HIV Prevention Trials Network (HPTN) known as HPTN 096. It aims to reduce HIV rates among Black men who have sex with men in the southern United States using a strategy developed based on what communities have told Dr. Nelson and colleagues is needed to do so. As a result, the study includes a package of four interventions which simultaneously address social, structural, institutional, and behavioral barriers to HIV prevention and care. HPTN 096 will soon launch in Atlanta, south Florida, Montgomery, Memphis, and Dallas.

More HIV Research Updates to Follow on HIV.gov

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

A messenger RNA (mRNA) vaccine designed to prevent human cytomegalovirus (CMV) elicited long-lasting CMV-specific responses from several types of immune cells, outperforming a previous vaccine concept in multiple measures in a NIAID-supported laboratory study. The findings were published in the Journal of Infectious Diseases.

CMV has been present in much of the global population for centuries. Most people with CMV experience no symptoms and are unaware that they are living with the virus, but CMV is dangerous for people with compromised immune systems and for babies. It is the most common infectious cause of birth defects in the United States. When babies acquire CMV through birth it is called congenital CMV, and it affects about 1 out of every 200 children. Of babies with CMV, about 1 in 5 will experience long-term health effects, including hearing or vision loss, developmental and motor delays, seizures, or microcephaly (a small head). Infants born before 30 weeks’ gestational age or with low weight for age that have CMV may be susceptible to additional complications.

There is no preventive vaccine for CMV, and treatment options are limited. An effective CMV vaccine could present needless suffering for millions of babies, and research has been progressing for decades. A recent vaccine candidate was designed to use a laboratory-developed protein from CMV’s surface called glycoprotein B (gB)—known to assist CMV in fusing with and entering human cells—to safely teach the immune system how to respond to CMV exposure without causing disease. The vaccine provided about 50% protection from CMV in Phase 2 trials, but that effect was insufficient for the concept to advance to large efficacy studies. 

A different, mRNA-based, vaccine is now in a Phase 3 efficacy study in cisgender women with no existing CMV infection. The vaccine was designed to instruct cells to produce the gB protein while also producing a combination of five other glycoproteins on CMV’s surface, which like gB are involved in human cell entry.

To better understand how the mRNA vaccine might perform in comparison to gB-based vaccine, researchers examined the immune cells present in blood samples provided by people when they participated in previous studies of each vaccine. The study team performed several assays—laboratory tests—and made the following key observations:

• The mRNA vaccine generated higher levels of antibodies to the five glycoproteins unique to the that vaccine in the form of immunoglobulin G (IgG) antibodies, which are associated with long-term immunity.
• The mRNA vaccine generated more potent signals that the immune system was prepared to deploy antibodies to surround and neutralize—destroy—CMV.
• The gB-based vaccine generated higher levels of IgG antibodies to gB.
• Immune responses to both vaccines were greater in study participants with no existing CMV, but the vaccines still amplified immune system activity in people already living with the virus. 

The authors concluded that the mRNA vaccine concept showed promise for better performance than its predecessor in ongoing clinical studies, of which results are expected soon. These results also highlight an opportunity to reformulate the mRNA vaccine to increase the amount of gB proteins it generates, which in tun could improve gB-specific immune responses.

This work was led by Weill Cornell Medicine in collaboration with the Duke Human Vaccine Institute at Duke University Medical Center, Vanderbilt University, Cincinnati Children’s Hospital Medical Center, and Moderna, Inc. in Cambridge, Mass. Moderna co-funded the research with NIAID.

Reference: X Hu, et al. Human Cytomegalovirus mRNA-1647 Vaccine Candidate Elicits Potent and Broad Neutralization and Higher Antibody-Dependent Cellular Cytotoxicity Responses Than the gB/MF59 Vaccine. Journal of Infectious Diseases DOI: 10.1093/infdis/jiad593 (2024).