HIV-1 and HIV-2 are the two distinct types of human immunodeficiency virus, and they differ in origin, severity, geographic spread, and response to treatment. HIV-1 is responsible for the vast majority of infections worldwide, while HIV-2 is uncommon, slower progressing, and mostly concentrated in West Africa. As of 2024, roughly 40.8 million people globally were living with HIV, with HIV-1 accounting for nearly all of those cases.
Different Animal Origins
Both viruses jumped from primates to humans, but from different species. HIV-1 originated in chimpanzees (specifically the subspecies found in west central Africa), with at least four separate cross-species transmissions to humans. One or two of those transmissions may have passed through gorillas first. A strain of HIV-1 discovered more recently, called group P, is very closely related to gorilla viruses and most likely resulted from a direct gorilla-to-human jump.
HIV-2 came from a different primate entirely: the sooty mangabey, a monkey native to West Africa. Multiple mangabey-to-human transmissions occurred independently, which is why several distinct lineages of HIV-2 exist. These separate origins explain why HIV-1 and HIV-2, while causing a similar disease, behave quite differently in the human body.
Where Each Type Is Found
HIV-1 circulates on every continent and drives the global epidemic. HIV-2 remains largely confined to West Africa, with the highest rates reported in Guinea-Bissau, Cabo Verde, Burkina Faso, Côte d’Ivoire, and Mali. Cases outside that region are rare and typically linked to migration from endemic areas. France, because of historical ties to West Africa, has a notable number of HIV-2 cases compared to other European countries. Surveillance and diagnostic testing for HIV-2 remain limited in many parts of the world, so the true burden is likely underestimated.
How Severity and Progression Differ
HIV-2 is generally milder and far less likely to progress to AIDS. Many people with HIV-2 live for decades without developing serious immune damage, and some never progress at all. HIV-1, by contrast, follows a more aggressive course. Without treatment, most people with HIV-1 develop AIDS within roughly 8 to 10 years.
This difference in virulence extends to transmission. HIV-2 is about five times less likely to spread through sexual contact compared to HIV-1. The gap is even wider for mother-to-child transmission: HIV-2 carries a 20- to 30-fold lower risk of passing from mother to baby during pregnancy and birth. Among mothers with HIV-2 who received no treatment, the pooled transmission rate was just 0.2%, compared to rates that can exceed 15 to 30% for untreated HIV-1. Because HIV-2 produces lower levels of virus in the blood and causes less viral shedding, it is simply harder to pass on.
Testing and Diagnosis
Standard HIV screening tests detect both types, but telling them apart requires an additional step. In the U.S., the recommended approach uses a combination test that first screens for HIV antibodies and antigens, then follows up with a differentiation assay (such as the Bio-Rad Multispot rapid test) that identifies whether the antibodies are reacting to HIV-1, HIV-2, or both. If the result is ambiguous, the lab dilutes the sample and retests to pin down which virus is present.
Getting this distinction right matters because treatment differs between the two types. In areas where HIV-2 is uncommon, clinicians may not think to confirm which type a person has, which can lead to the wrong treatment approach.
Treatment Differences
One of the most important practical differences between HIV-1 and HIV-2 is how they respond to medication. A major class of antiretroviral drugs, non-nucleoside reverse transcriptase inhibitors (commonly abbreviated NNRTIs), works well against HIV-1 but is essentially useless against HIV-2. This is not acquired resistance from drug exposure. HIV-2 is structurally different in the exact spot where these drugs bind, so the medications simply cannot attach and do their job. The shape of a single amino acid in HIV-2’s enzyme blocks the drug from fitting into place.
Other drug classes work against both viruses. Nucleoside-based drugs (NRTIs) that act as chain terminators have broad activity against HIV-1 and HIV-2 alike. Integrase inhibitors, which block the virus from inserting its genetic material into human cells, are highly effective against HIV-2 in lab studies and clinical use. Dolutegravir, one of the most widely used integrase inhibitors, has shown strong results in treatment-naive HIV-2 patients, achieving undetectable viral loads.
Monitoring HIV-2 treatment is more complicated than for HIV-1. There is no FDA-approved commercial test to measure HIV-2 viral load. In New York State, clinicians can send samples to the Wadsworth Center Bloodborne Viruses Laboratory for specialized testing, but access is limited elsewhere. When viral load testing is unavailable, doctors watch for sustained drops in immune cell counts or worsening symptoms as signs that treatment may be failing.
Dual Infection With Both Types
It is possible to carry both HIV-1 and HIV-2 at the same time. In a Spanish registry of 373 people with HIV-2, about 9% were coinfected with HIV-1. Dual infection tends to look more like HIV-1 infection in terms of severity: coinfected individuals in that study had lower immune cell counts (a median of 204 cells per microliter, well below the healthy range) and were more likely to have experienced AIDS-defining illnesses compared to those with HIV-2 alone.
Treatment for dual infection requires careful drug selection to cover both viruses, since NNRTIs would leave HIV-2 unchecked. With appropriate therapy, about 70% of dually infected patients in the Spanish study achieved viral suppression for both viruses, and median immune cell counts rose to 418 cells per microliter after roughly two and a half years of treatment. For anyone from a region where HIV-2 is common, testing should confirm whether one or both types are present at the time of initial diagnosis.