UPDATE COMING We’re currently working to update this article. Studies have shown that a person living with HIV who is on regular antiretroviral therapy that reduces the virus to undetectable levels in the blood is NOT able to transmit HIV to a partner during sex. This page will be updated soon to reflect the medical consensus that “Undetectable = Untransmittable.”

Viral load is the level of HIV in your blood. Uninfected people have no viral load. If you test positive for HIV, your healthcare team may use viral load testing to monitor your condition.

Your viral load shows how active HIV is in your system. Usually, if your viral load is high, your CD4 count is low. CD4 cells (T cells) help activate your immune response. HIV attacks and destroys CD4 cells, which reduce your body’s response to the virus.

A low or undetectable viral load indicates your immune system is actively working to help keep HIV in check. Knowing these numbers helps determine your treatment.

The first viral load blood test is usually performed soon after a diagnosis of HIV. This test is helpful before and after a change in medication. Your doctor may order follow-up testing at regular intervals to see whether your viral load changes over time.

A growing viral count means your infection is worsening, and changes to your current therapies may be needed. A downward trend in viral load is a good sign.

Antiretroviral therapy (ART) is medication that helps to keep the viral load in your body under control. For many people, HIV treatment can substantially lower viral load levels, sometimes to undetectable levels. Your viral load is considered undetectable if your test shows lower than 40 to 75 HIV virus particles in a milliliter of your blood. If your viral load is considered undetectable it means your medication is working.

A word of caution: “undetectable” doesn’t mean the virus particles aren’t there, or that you no longer have HIV. It simply means that your viral load is so low that the test is unable to measure it. You should continue to take ART to remain healthy and keep your viral load undetectable.

Studies show that there may be temporary viral load spikes, sometimes called “blips.” These spikes can happen even in people who have had undetectable viral load levels for an extended period.

These increased viral loads may occur between tests, and there may be no symptoms. Also, viral load levels in blood or genital fluids or secretions are often similar. But a person with an undetectable blood viral load can have a higher level of virus in genital fluids or secretions.

A low viral load means you are less infectious. But it’s important to note that the viral load test only measures the amount of HIV that is in your blood. An undetectable viral load doesn’t mean HIV isn’t present in your body.

HIV can still be transmitted to a sexual partner through seminal fluid or vaginal or anal secretions when your viral load is considered undetectable.

Continue to take precautions to lower the risk of transmission. Make sure to use condoms correctly and consistently when having sex.

It is also possible to transmit HIV to partners by sharing needles. It is never safe to share needles.

Have an open and honest discussion with your partner, and ask your doctor to explain viral load and the risks of HIV transmission.


Some sources say that the chances of transmitting HIV with an undetectable viral load is zero. Is this true?


While some experts have gone on record indicating that your chances of contracting HIV from someone who is on ‘durable’ antiretroviral therapy (ART) are zero, the authors of the quoted study didn’t conclude that transmission risk was zero nor did they advocate unprotected sex among these couples. The authors of the study noted that eight partners became infected.

The CDC also still doesn’t endorse this position and continues to caution that ‘a person with HIV can still potentially transmit HIV to a partner, even if they have an undetectable viral load.’

Timothy J. Legg, PhD, CRNPAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

More about this study: Experts who have gone on record quote a study published in the New England Journal of Medicine in September 2016 about HIV-1 transmission. The study concluded that early initiation of antiretroviral therapy “led to a sustained decrease in genetically linked HIV-1 infection in sexual partners.” But it doesn’t eliminate all cases of transmission in couples where one is HIV-positive.

The authors of the study also noted that eight members of the discordant couples became infected. They speculated that “four of these infections probably occurred before the infection was virally suppressed in the index participant,” but this is not certain. In the case of the other four infections, they noted that the “partner infection occurred after ART failed in the index participant.”

Taking ART during your pregnancy and delivery can greatly reduce your risk of passing on HIV to your child. Having an undetectable viral load is the goal during pregnancy.

Women can take HIV medicines safely during pregnancy, but talk to your doctor about specific regimens. If you are already taking ART, pregnancy may affect how your body processes your medicine. Certain changes in your treatment might be needed.

The amount of the viral load of people infected with HIV in a specific group is called community viral load (CVL). A high CVL may put people within that community who don’t have HIV at greater risk of contracting the virus.

CVL can be a valuable tool in determining which HIV treatments effectively lower viral load. CVL may be useful in learning how lower viral load may affect transmission rates within specific communities or groups of people.

Having a viral load that is undetectable greatly lowers your chances of transmitting HIV to your sexual partners or partners you might share needles with. Additionally, the Centers for Disease Control and Prevention (CDC) reports that treatment of pregnant women with HIV and their babies reduces viral load count and risk of mother-to-infant transmission.

In general, early treatment has been shown to reduce the viral load count in the blood of people with HIV. Besides lowering the rates of transmission to people who don’t have HIV, early treatment and lower viral load is helping people with HIV live longer, healthier lives.