Did you know that there are two types of human immunodeficiency virus (HIV)? Besides the more common HIV-1, there’s also HIV-2, which is not as widespread but just as important when it comes to understanding HIV/AIDS. HIV-1 attacks the body’s immune cells, and if someone gets both HIV-1 and HIV-2, it’s called dual infection.

Unlike some diseases when having one type might protect you from another, that’s not the case with HIV. If you get sick with one type of the flu, your body might be better at fighting off similar types in the future. But with HIV, getting one type doesn’t make you safe from the other. The problem is, HIV-2 is not as common, and it’s hard to diagnose both kinds at once. Because of this, there’s not much information about people who have both types of HIV, which makes it difficult for scientists to study.

HIV-1 and HIV-2 share less than half of their genetic makeup. Plus, they have different ways of working and causing harm to the body. HIV-1 and HIV-2 affect various groups of people, are diagnosed using different tests, and may require different treatments. Most people with HIV have HIV-1 infection.

Who Has HIV-1 and HIV-2?

About 19 out of 20 people with HIV infection worldwide have HIV-1. This virus is found throughout the world.

HIV-2 is most common in West African countries. It has also caused a small number of infections in people in Europe, Asia, Oceania, North America, South America, and the Caribbean. Only 0.06 percent of people with HIV in the United States have the HIV-2 subtype.

In places where both viruses can occur, it’s possible to have both HIV-1 and HIV-2 infections. These dual infections primarily occur in West Africa, where up to 1 out of 10 people with HIV have both viruses.

HIV-1 and HIV-2 Subtypes

HIV-1 has four unique groups (M, N, O, P), each coming from a separate event where it jumped from animals to humans. Group M (main) is the most common type of HIV-1 worldwide, which can also be broken down into nine additional subtypes (A-D, F-H, J-K). HIV-2 is divided into A and B subtypes. Sometimes, different subtypes can combine to form a brand-new subtype.

These different subtypes are more or less common in various parts of the world, but all HIV-1 subtypes and all HIV-2 subtypes are generally treated the same.

How Does Each Virus Spread?

Both types of HIV are transmitted (spread) in similar ways, including through:

• Sexual contact
• Exposure to blood that contains the virus
• Pregnancy, birth, or breastfeeding

HIV-2 is less likely to spread through these methods. The lower chance of spreading HIV-2 might be due to its lower virus levels in people with HIV-2 compared to those with HIV-1. For example, untreated mothers with HIV-1 have a 15 percent to 30 percent chance of transmitting the virus to their child during pregnancy or birth. The risk is 1 percent to 2 percent for mothers with untreated HIV-2.

Symptoms of HIV-1 and HIV-2

Both types of HIV lead to similar symptoms, although those with HIV-2 typically have a longer phase when they don’t have any symptoms.

In HIV’s early stages, people with HIV-1 or HIV-2 may experience:

• Fever, chills, or night sweats
• Muscle aches
• Coughing
• Rash
• Sore throat
• Diarrhea

Once these symptoms disappear, people will then enter the chronic or clinical latent stage of HIV (long-term or quiet phase). In this stage, the virus is within the CD4 cells, a type of white blood cell, but no symptoms appear.

Those with HIV-2 tend to stay in this long-term stage for about twice as long as those with HIV-1. These people are also more likely to have a lower viral load (fewer viral particles in the body), which means that their immune system may not be damaged as quickly or as severely. Their condition may take longer or may never progress to the third HIV stage, AIDS, in which the immune system can be very weak and serious infectious diseases may occur.

People with AIDS have low CD4 counts and tend to have similar signs and symptoms regardless of whether they have HIV-1 or HIV-2.

Diagnosing HIV-1 and HIV-2

Several types of tests are used to diagnose HIV, with some differences in the tests between the two HIV types.

Experts such as the Centers for Disease Control and Prevention (CDC) recommend that testing for HIV should include a sequence of tests to look for both HIV-1 and HIV-2. They suggest that doctors first perform an HIV antigen/antibody test. This test can show whether a person’s blood contains pieces of the HIV-1 or HIV-2 viruses or antibodies (proteins made by the immune system to try to fight the virus) to one or both.

If this test result is positive, it indicates that someone may have HIV, and further testing is needed for confirmation. The CDC then recommends that labs perform an HIV-1/HIV-2 differentiation immunoassay. This test can confirm the infection and distinguish between the two main virus types, showing whether there is HIV-1, HIV-2, or both. The differentiation assay may also suggest whether the antigen/antibody assay test result might have been false-positive, and there is no HIV infection.

If the antigen/antibody assay test result is positive, but the differentiation assay result is negative, more testing is done to rule out acute HIV infection. This is done by testing for HIV-1 genetic material (RNA) with a nucleic acid amplification test (NAAT). However, an HIV-2 NAAT is not routinely available to test for HIV-2, and further testing may be needed if a person is at risk for this infection.

Diagnosing HIV-1 and HIV-2 infection is recommended by the testing sequence just mentioned. But if these are not done first and instead someone has a strongly positive HIV-1 and/or HIV-2 NAAT result alone, showing a high amount of RNA or DNA in the blood, these suggest HIV-1 or HIV-2 infection are present and should be confirmed with the other testing. A negative HIV-1 or HIV-2 NAAT result alone, however, is not adequate to rule out infection, as some people can have negative test results with this assay but still have active infection.

HIV-1 and HIV-2 Treatments

Doctors recommend that almost everyone with HIV infection take antiretroviral therapy (ART). This treatment blocks the virus from making more copies of itself, which helps the body keep the infection under control and reduces the risk of having HIV spread to other people. The only times when HIV treatment may not be recommended is if the person’s body is controlling the HIV well enough on its own and the HIV NAAT blood test result is negative or undetectable.

There are many types of ART that work very well for people with HIV-1. In the past, ART medications were mainly available only in pill form taken every day. More recently, however, people with HIV-1 have the option of taking ART via injectable therapy, which is administered monthly.

HIV-2 is resistant to certain ART types — including fusion inhibitors like enfuvirtide (Fuzeon) and a class of medications called non-nucleoside reverse transcriptase inhibitors. These medications will not work in people with HIV-2.

Those with HIV-2 will be treated with other common types of ART medications, including integrase strand transfer inhibitors, nucleoside reverse transcriptase inhibitors, and protease inhibitors. Researchers are also evaluating whether injectable ART therapies, when combined with other treatments, may be effective in people with HIV-2.

In people with HIV-1 or HIV-2, the virus may undergo additional gene changes that cause drug resistance to develop. These individuals may have to switch their treatment regimens.

Outlook and Complications

Because HIV-2 often leads to a lower viral load and has a slower disease progression (takes longer to transform into AIDS), it is often linked to a better outlook. A study of one group in West Africa, before the widespread availability of highly effective ART, showed that people with HIV-2 lived twice as long as those with HIV-1. However, HIV-2 can still cause AIDS and be fatal, so treatment is still important.

The two types of HIV can sometimes lead to different sets of complications — problems that arise as a result of the infection. Those with HIV-2 are less likely to develop Kaposi sarcoma, a type of cancer that causes tumors to form in the body’s soft tissues.

HIV-1 and HIV-2 Vaccination

Vaccines teach your immune system to fight off certain types of germs, including viruses. Researchers are currently working on HIV vaccines that could help prevent infection.

Because the HIV-1 and HIV-2 viruses are not the same, they will likely require different vaccines. If HIV vaccines are developed, different vaccines may need to be used in various countries depending on which types are most common there.

Talk With Others Who Understand

On myHIVteam, the social support network for people with HIV and their loved ones, more than 40,000 members come together to ask questions, give advice, and share their stories with others who understand life with HIV.

Do you know if you have HIV-1 or HIV-2? Share your experience in the comments below, or start a conversation by posting on your Activities page.