When transmission happens

Mother-to-child transmission, also called vertical transmission, can happen during pregnancy, childbirth or breastfeeding. But a mother having HIV does not mean her baby will necessarily acquire it.

How prevention works

The first step is HIV testing during pregnancy, so treatment can start early. Antiretroviral therapy, or ART, suppresses the virus and lowers the mother's viral load: the amount of HIV in her blood. This protects her health and greatly reduces the risk of transmission to the baby.

Prevention continues after birth. The baby receives preventive antiretroviral medicine and HIV testing, and the mother needs continued treatment and follow-up. Infant feeding also needs individual advice: treatment reduces transmission through breastfeeding, but does not make that risk zero.

What the figures show

Worldwide, estimated new HIV infections in children fell from 300,000 in 2010 to 93,000 in 2025: a decline of 69%. Wider access to testing and treatment during pregnancy has been central to that progress.

The EU and European Economic Area still reported 196 diagnoses attributed to mother-to-child transmission in 2024. That was 1.1% of diagnoses with a known transmission route. Estonia reported one such diagnosis in 2023. These are diagnosis counts, not necessarily infections acquired locally that year.

Mother-to-child transmission, also called vertical transmission, can occur during pregnancy, childbirth, or breastfeeding. However, a mother having HIV does not mean that her baby will necessarily acquire the infection.

The first step in prevention is HIV testing during pregnancy, so treatment can begin as early as possible. Antiretroviral therapy, or ART, suppresses HIV replication and lowers the mother’s viral load — the amount of HIV in her blood. This protects the mother’s health and greatly reduces the risk of transmission to the baby.

Prevention also continues after birth. The baby may receive preventive antiretroviral medicine and undergo HIV testing, while the mother continues treatment and follow-up. Infant feeding also requires individual guidance. Effective treatment reduces the risk of transmission through breastfeeding, but does not reduce it to zero.

Globally, estimated new HIV infections in children fell from 300,000 in 2010 to 93,000 in 2025, which is a decline of about 69%. Wider access to HIV testing and treatment during pregnancy has played a major role in this progress.

However, mother-to-child transmission has not disappeared completely. In the EU and European Economic Area, 196 HIV diagnoses in 2024 were attributed to mother-to-child transmission. This represented 1.1% of diagnoses where the transmission route was known. Estonia reported one such diagnosis in 2023. These figures refer to diagnoses, so they do not necessarily mean that the infections were acquired locally or during that same year.

• Mother-to-child transmission, also called vertical transmission, can occur during pregnancy, childbirth, or breastfeeding.
• A mother having HIV does not mean that her baby will necessarily acquire it, especially when HIV is diagnosed and treated early.
• HIV testing during pregnancy is important because it allows antiretroviral therapy, or ART, to begin as soon as possible.
• ART suppresses HIV replication and lowers the mother’s viral load, meaning the amount of HIV in her blood. This protects her health and greatly reduces the risk of transmission to the baby.
• Prevention continues after birth, with HIV testing and preventive antiretroviral medicine for the baby, while the mother continues treatment and follow-up.
• Infant feeding also requires individual guidance because treatment greatly reduces transmission through breastfeeding, but does not make the risk completely zero.
• Globally, estimated new HIV infections in children fell from 300,000 in 2010 to 93,000 in 2025, which is a decline of about 69%.
• This progress is largely linked to wider access to HIV testing and treatment during pregnancy.
• In the EU and European Economic Area, 196 HIV diagnoses in 2024 were attributed to mother-to-child transmission, representing 1.1% of diagnoses where the transmission route was known.
• Estonia reported one such diagnosis in 2023. These figures are diagnosis counts, so they do not necessarily show where or when the infection was acquired.

PrEP: before exposure

Medicines can also prevent HIV in someone who does not have it. The main difference between PrEP and PEP is when they are used.

PrEP means pre-exposure prophylaxis. Prophylaxis simply means prevention. It is taken before a possible exposure, so protective drug levels are already present when needed. It can suit someone with an ongoing risk of acquiring HIV.

PrEP needs a medical assessment, a negative HIV test before starting, and regular testing while it is used. It is not a vaccine, and protection depends on taking it according to the prescribed schedule.

PEP: after exposure

PEP means post-exposure prophylaxis. This is emergency prevention after a possible exposure, such as a needlestick injury or a condom breaking when there may have been an HIV risk.

It should start as soon as possible, ideally within 24 hours and no later than 72 hours. The course lasts 28 days. The point is to interrupt infection early, so we do not wait for symptoms or for a test to turn positive.

What both require

Both need correct use and follow-up. They prevent HIV, not other sexually transmitted infections, so condoms and other prevention measures still matter. In short: PrEP is planned prevention; PEP is an emergency response.

Antiretroviral medicines can also be used to prevent HIV in people who do not have the infection. The main difference between PrEP and PEP is when they are used.

PrEP means pre-exposure prophylaxis. Prophylaxis simply means prevention. PrEP is taken before a possible exposure to HIV, so protective levels of the medicine are already present when they are needed. It can be suitable for people who have an ongoing risk of acquiring HIV.

Before starting PrEP, a person needs a medical assessment and a negative HIV test. Regular HIV testing is also required while PrEP is being used. PrEP is not a vaccine, and its effectiveness depends on taking it according to the prescribed schedule.

PEP means post-exposure prophylaxis. Unlike PrEP, it is used as an emergency measure after a possible HIV exposure — for example, after a needlestick injury or condom failure when there may have been a risk of HIV transmission.

PEP should be started as soon as possible, ideally within 24 hours and no later than 72 hours after exposure. The treatment course lasts 28 days. The aim is to stop HIV from establishing infection at an early stage, which is why treatment should not be delayed while waiting for symptoms or for an HIV test to become positive.

Both PrEP and PEP require correct use and appropriate follow-up. They prevent HIV, but not other sexually transmitted infections, so condoms and other preventive measures can still be important.

In simple terms: PrEP is planned prevention before exposure; PEP is an emergency response after exposure.

• Antiretroviral medicines can also prevent HIV in people who do not have the infection, and the main difference between PrEP and PEP is when they are used.
• PrEP means pre-exposure prophylaxis and is taken before a possible exposure to HIV, so protective drug levels are already present when needed.
• PrEP can be suitable for someone who has an ongoing risk of acquiring HIV.
• Before starting PrEP, a person needs a medical assessment and a negative HIV test, followed by regular testing while using it.
• PrEP is not a vaccine, and its effectiveness depends on taking it according to the prescribed schedule.
• PEP means post-exposure prophylaxis and is used as emergency prevention after a possible exposure, such as a needlestick injury or condom failure.
• PEP should be started as soon as possible, ideally within 24 hours and no later than 72 hours after exposure.
• The treatment course lasts 28 days, and the aim is to stop HIV from establishing infection before it becomes permanently established in the body.
• Because of this, PEP should not be delayed while waiting for symptoms or for an HIV test to become positive.
• Both PrEP and PEP prevent HIV, but not other sexually transmitted infections, so other prevention methods can still be important.
• In simple terms, PrEP is planned prevention before exposure, while PEP is emergency prevention after exposure.

Oral PrEP: two medicines

A commonly used oral PrEP combination is tenofovir disoproxil fumarate and emtricitabine, shortened to TDF/FTC. The slash means two medicines in one combination, not one drug with two names.

Both target reverse transcriptase, the HIV enzyme that makes a DNA copy from the virus's RNA. They belong to the nucleoside or nucleotide reverse transcriptase inhibitor group, usually called NRTIs. Blocking this step makes it harder for HIV to establish infection.

PEP: an additional target

The PEP example here uses the same two medicines plus dolutegravir. Dolutegravir targets a different HIV enzyme, integrase, which normally inserts viral DNA into the infected cell's DNA.

So this regimen contains three medicines acting at two different steps: making viral DNA, and inserting it into the host genome. Dolutegravir is an integrase strand transfer inhibitor, or INSTI.

Why the distinction matters

This is one example of a PEP regimen, not the only option. The choice depends on clinical assessment, including other medicines and kidney function. Also, the two-drug TDF/FTC PrEP combination alone is not a complete treatment regimen for established HIV. That is one reason testing before PrEP matters.

A commonly used oral PrEP combination is tenofovir disoproxil fumarate and emtricitabine, usually shortened to TDF/FTC. These are two separate medicines used together in one combination.

Both drugs target reverse transcriptase, an HIV enzyme that converts the virus’s RNA into DNA. They belong to the nucleoside or nucleotide reverse transcriptase inhibitor group, commonly called NRTIs. By interfering with this process, they make it much more difficult for HIV to establish an infection.

The PEP example shown here contains the same two medicines, TDF and FTC, together with dolutegravir.

Dolutegravir acts at a different stage of the HIV life cycle. It targets integrase, the viral enzyme that normally inserts newly produced HIV DNA into the DNA of the infected cell.

So this PEP regimen contains three medicines acting at two different stages of viral replication: TDF and FTC interfere with the production of viral DNA, while dolutegravir prevents that DNA from being integrated into the host genome. Dolutegravir belongs to a group called integrase strand transfer inhibitors, or INSTIs.

This is one example of a PEP regimen rather than the only possible option. The exact choice depends on clinical factors such as other medications, kidney function, and the circumstances of the exposure.

It is also important to remember that TDF/FTC alone is not a complete treatment regimen for established HIV infection. This is one reason why HIV testing before starting PrEP is essential.

• A commonly used oral PrEP combination is tenofovir disoproxil fumarate and emtricitabine, usually shortened to TDF/FTC.
• TDF and FTC both target reverse transcriptase, the HIV enzyme that converts the virus’s RNA into DNA.
• They belong to the group called nucleoside or nucleotide reverse transcriptase inhibitors, or NRTIs.
• By interfering with reverse transcriptase, these medicines make it much harder for HIV to produce the DNA copy it needs to establish infection.
• The PEP example shown here contains TDF and FTC together with dolutegravir.
• Dolutegravir acts on another viral enzyme called integrase, which normally inserts HIV DNA into the DNA of the infected cell.
• Dolutegravir belongs to the group called integrase strand transfer inhibitors, or INSTIs.
• This means the PEP regimen uses three medicines acting at two different stages of the HIV life cycle: TDF and FTC interfere with viral DNA production, while dolutegravir blocks integration.
• This is one example of a PEP regimen, and the exact choice can depend on factors such as other medications, kidney function, and the circumstances of the exposure.
• It is also important that TDF/FTC alone is not a complete treatment regimen for established HIV, which is one reason HIV testing before starting PrEP is necessary.

First: RNA becomes DNA

Following the diagram from left to right, HIV carries its genetic information as RNA. After entering a CD4 T cell, it uses reverse transcriptase to build a DNA copy. CD4 T cells are helper T cells, which help coordinate immune responses.

Think of DNA synthesis as adding building blocks, or nucleotides, one at a time. Tenofovir and emtricitabine are converted into active forms inside cells. These resemble normal DNA building blocks and compete with them.

If reverse transcriptase adds one of these drug molecules to the growing viral DNA, the chain cannot extend normally. This is chain termination. The medicines interfere with making the DNA copy; they do not simply destroy every virus particle.

Then: viral DNA is inserted into host DNA

If HIV has made its DNA copy, integrase normally inserts it into the cell's DNA. The integrated viral instructions can then be used by the cell to make components of new viruses.

Dolutegravir blocks this insertion step. It does not remove HIV DNA that has already integrated. That difference helps explain why preventing infection and treating established HIV are not quite the same situation.

The two targets

Tenofovir and emtricitabine interrupt DNA copying; dolutegravir interrupts DNA integration. They act on viral enzymes, rather than relying only on the immune system to recognise HIV.

Following the diagram from left to right, HIV carries its genetic information as RNA. After entering a CD4 T cell, the virus uses the enzyme reverse transcriptase to create a DNA copy of its RNA. CD4 T cells are helper T cells that play an important role in coordinating immune responses.

DNA is built by adding small building blocks called nucleotides one at a time. Inside cells, tenofovir and emtricitabine are converted into active forms that resemble these normal DNA building blocks.

Because they look similar, reverse transcriptase can mistakenly incorporate them into the growing viral DNA chain. When this happens, the DNA chain can no longer continue normally. This process is called chain termination.

So tenofovir and emtricitabine do not simply destroy HIV particles. Instead, they interfere with the virus’s ability to make a complete DNA copy of its genetic material.

If HIV successfully produces its DNA, the next important step involves integrase. This enzyme normally inserts the viral DNA into the DNA of the infected cell. Once integrated, the viral genetic instructions can be used by the cell to produce components for new virus particles.

Dolutegravir blocks this integration step. However, it does not remove HIV DNA that has already become integrated into the host genome.

So the main idea is straightforward: tenofovir and emtricitabine interrupt viral DNA synthesis, while dolutegravir interrupts viral DNA integration. Together, these medicines target essential viral enzymes at different stages of the HIV life cycle.

• This diagram shows more clearly where these medicines act in the HIV life cycle.
• HIV carries its genetic information as RNA, and after entering a CD4 T cell it uses reverse transcriptase to make a DNA copy.
• CD4 T cells are helper T cells that help coordinate immune responses.
• DNA is built by adding small building blocks called nucleotides one at a time.
• Inside cells, tenofovir and emtricitabine are converted into active forms that resemble normal DNA building blocks.
• Reverse transcriptase can mistakenly add these drug molecules into the growing viral DNA chain.
• When that happens, the DNA chain cannot continue normally, producing what is called chain termination.
• So TDF and FTC do not simply destroy virus particles; instead, they interfere with HIV’s ability to produce a complete DNA copy.
• If HIV successfully makes its DNA, integrase normally inserts that viral DNA into the cell’s own DNA.
• Dolutegravir blocks this integration step, preventing the viral DNA from being inserted into the host genome.
• However, dolutegravir does not remove HIV DNA that has already been integrated.
• The key idea is therefore: tenofovir and emtricitabine interrupt viral DNA synthesis, while dolutegravir interrupts viral DNA integration.

Testing comes first

Prevention also depends on finding HIV early. A person can have HIV and feel completely well, so symptoms are not a reliable guide. Testing allows treatment to start before substantial immune damage develops.

A negative test immediately after an exposure does not necessarily rule out infection. Tests have a window period: the time before they can reliably detect it. That is why the timing of testing and, when needed, repeat testing matter.

Access in Estonia

In Estonia, HIV counselling and testing centres offer free, anonymous testing, including for people without health insurance. Anonymous means you do not have to give your name. That removes practical barriers, but people also need to know the service exists.

What U=U means

Treatment benefits both the person and their partners. U=U means undetectable equals untransmittable. Someone who takes effective treatment and maintains an undetectable viral load does not transmit HIV sexually.

Viral load measures how much HIV RNA is in the blood. It is different from a CD4 count, which measures immune cells. By suppressing HIV replication, treatment helps preserve those cells and immune function.

What U=U does not mean

Undetectable does not mean cured, and the protection is not immediate after the first tablet. It depends on achieving and maintaining suppression, with continued treatment and monitoring. U=U refers to sexual transmission; it should not be extended to breastfeeding or protection from other sexually transmitted infections.

Effective HIV prevention also depends on finding infections early. A person can have HIV and feel completely healthy, especially during the early stages, so symptoms alone are not a reliable way to determine whether someone has been infected.

Testing allows HIV to be diagnosed and treatment to begin before major damage to the immune system develops.

However, a negative HIV test immediately after a possible exposure does not always rule out infection. HIV tests have a window period, which is the time between infection and the point when a test can reliably detect it. Because of this, the timing of testing — and sometimes repeat testing — is important.

In Estonia, HIV counselling and testing centres provide free and anonymous HIV testing, including for people without health insurance. Anonymous testing means that a person does not need to provide their name, which helps reduce practical barriers to testing.

Treatment is important not only for the person living with HIV, but also for preventing transmission to others. This brings us to U=U: undetectable equals untransmittable.

When a person takes effective antiretroviral treatment and maintains an undetectable viral load, they do not transmit HIV through sex.

Viral load refers to the amount of HIV RNA present in the blood. This is different from the CD4 count, which measures the number of CD4 immune cells. By suppressing viral replication, ART lowers the viral load and helps preserve CD4 cells and normal immune function.

However, undetectable does not mean cured. Viral suppression is also not achieved immediately after the first dose of treatment. U=U depends on reaching and maintaining an undetectable viral load through continued treatment and monitoring.

Finally, U=U specifically refers to sexual transmission of HIV. It should not be extended to situations such as breastfeeding, and it does not provide protection against other sexually transmitted infections.

• HIV prevention also depends on finding infections early because a person can have HIV and feel completely healthy.
• Symptoms are therefore not a reliable way to know whether someone has been infected.
• Testing allows treatment to begin before significant damage to the immune system develops.
• However, a negative test immediately after an exposure does not always rule out HIV because tests have a window period.
• The window period is the time between infection and the point when a test can reliably detect it, so the timing of testing and sometimes repeat testing are important.
• In Estonia, HIV counselling and testing centres provide free and anonymous HIV testing, including for people without health insurance.
• Anonymous testing means that a person does not need to provide their name, which helps reduce barriers to testing.
• Treatment also prevents transmission to others, which leads to the concept of U=U: undetectable equals untransmittable.
• A person who takes effective treatment and maintains an undetectable viral load does not transmit HIV through sex.
• Viral load measures the amount of HIV RNA in the blood, while a CD4 count measures the number of CD4 immune cells.
• By suppressing HIV replication, treatment lowers the viral load and helps preserve CD4 cells and immune function.
• Undetectable does not mean cured, and viral suppression is not achieved immediately after starting treatment.
• U=U depends on reaching and maintaining an undetectable viral load through continued treatment and monitoring.
• U=U specifically refers to sexual transmission of HIV and should not be extended to breastfeeding or protection from other sexually transmitted infections.