Sexually Transmitted Infections

What is an STI?

STI stands for sexually transmitted infection (sexually transmitted disease, or STD, is also used.) People contract STIs through sexual contact with an infected person. Some STIs have other, nonsexual means of transmission. Risk of contracting STIs can be reduced by avoiding sexual contact, or by consistent use of condoms during sexual activity, or by practicing safer forms of sexual intimacy. In some cases, people can further reduce their risk of contracting a sexually transmitted infection by being vaccinated.

Which STIs have vaccines?

Some STIs, such as gonorrhea, Chlamydia, and syphilis, are caused by bacteria. They are usually effectively treated with antibiotics, although many patients do not know that they are infective and can spread the disease to other partners. The availability of treatments means vaccines against these diseases are not a top priority, although the increased resistance of gonorrhea to antibiotics may lead to a shift in priorities.

Viral STIs are often highly persistent despite current therapeutic options or have no acceptable treatment available. Therefore, vaccines for certain viral STIs are in use, and others are in development.

In Use: HPV Vaccines

Human papillomaviruses (HPV) belong to a large family of viruses, only some of which are sexually transmitted. This article will only discuss sexually transmitted HPV.

Most people who contract HPV have no symptoms, and they quickly clear the virus from their bodies. However, certain types of HPV cause genital warts in other people. Other HPV types are the main cause of cervical cancer, and some are associated with anal, penile, mouth, and throat cancers.

HPV is common: a recent study showed nearly 27% of women aged 14-59 tested positive for one or more strains of HPV. Rates for men are likely to be similar. Mathematical models have shown that more than 80% of women will have been infected with genital HPV by the time they reach age 50.

The U.S. Food and Drug Administration approved Gardasil (HPV4), a Merck vaccine for four types of HPV, in 2006. FDA approved another vaccine, Cervarix (HPV2) from GlaxoSmithKline, which protects against two types of HPV, in 2009. A nine-valent vaccine (HPV9, Gardasil 9) was approved in 2014. All HPV vaccines use just a protein from the shell of certain HPV types: they contain no viral RNA or DNA, and so cannot cause disease or replicate in the body.

In Use: Hepatitis B Vaccines

Hepatitis B is an illness caused by the hepatitis B virus (HBV) and transmitted via contact with infectious bodily fluids. It can be spread sexually, or through sharing injection drug use equipment, needle sticks, birth to an infected mother, contact with open sores or wounds of an infected person, and sharing razors or toothbrushes with an infected person. Symptoms of hepatitis B infection include fever, abdominal pain, and jaundice, among others. Up to 95% of adults infected with the virus recover and do not become chronically (permanently) infected. The others remain infected and are at risk for serious liver disease.

The picture is different for children: infants and children who become infected with hepatitis B are much more likely than adults to become chronically infected.

In Development: Genital Herpes Vaccines

Genital herpes is a viral infection caused by herpes simplex viruses. Some infected people may have few or no symptoms of illness, but many others experience blisters and sores in the genital area. The infection can remain in the body indefinitely, and sores can recur again and again.

Researchers have developed many experimental attenuated and inactivated herpes vaccines, starting in the 1930s and continuing through the 1970s, though none was effective enough to be approved and licensed.

The National Institute of Allergy and Infectious Diseases and pharmaceutical company GlaxoSmithKline co-sponsored a Phase 3 clinical trial of a candidate subunit herpes vaccine on nearly 8,000 women across the country. The vaccine had previously shown some promise in a certain subset of women. In September 2010, however, researchers reported the Phase 3 trial failed to show that the vaccine was effective. Another herpes candidate vaccine, sponsored by Sanofi Pasteur, uses the whole virus and is in pre-clinical studies.

As much as it would be useful to have a highly effective herpes simplex vaccine, the current options are unlikely to be broadly useful.

In Development: HIV Vaccines

Human immunodeficiency virus (HIV) is the agent that causes Acquired Immune Deficiency Syndrome (AIDS). HIV can be transmitted via sexual contact with an infected person. (HIV can also be transmitted by other types of contact with contaminated body fluids.)

When a person first contracts HIV, he may have a mild to moderate illness with fever. After these symptoms subside, the virus persists in a “stealth mode” and causes slow damage to the immune system. Medications can keep people healthy for many years, and perhaps even indefinitely. A person with HIV infection that has progressed to AIDS can also benefit from treatment with medicines. There can be substantial restoration of immune function while the patient remains on active treatment. A person with AIDS has great difficulty fighting other diseases because of damage to the body’s disease-fighting white blood cells.

Progress toward an HIV vaccine has been slow since the virus was isolated in 1983. Only three HIV vaccines have been tested in clinical efficacy trials. It is difficult to make a vaccine for HIV for several reasons: 

• HIV mutates, or changes, much more rapidly than most other viruses. Targeting a vaccine to a rapidly changing virus is a challenging task for vaccine researchers.
• HIV damages the cells of the immune system. But to be effective, a vaccine must trigger the immune system to fight the disease agent. So, a challenge for HIV vaccine researchers is to develop a vaccine for HIV that must interact with the immune system in a way that is very different from the natural behavior of the virus.

To date, researchers have developed several candidate HIV vaccines, but none has performed well enough in clinical trials to be approved.

In Conclusion

Researchers have developed vaccines for two sexually transmitted diseases. Ongoing efforts to develop vaccines for herpes and HIV may prove successful in the future.

Sources

• Centers for Disease Control and Prevention. DC. . Accessed 01/25/2018.
• CDC. . Epidemiology and Prevention of Vaccine-Preventable Diseases. (463 KB). Atkinson, W., Wolfe, S., Hamborsky, J., McIntyre, L., eds. 13th ed. Washington DC: Public Health Foundation, 2015. Accessed 01/25/2018.
• Cohen, J. Painful failure of promising genital herpes vaccine. Science. 15 October 2010 330:304.
• Clinical Trials. . Identifier NCT00057330. Updated September 30, 2016. Accessed 01/25/2018.
• CDC. . Accessed 01/25/2018.