Post-Exposure Prophylaxis (PEP)

Post-Exposure Prophylaxis (PEP) is an emergency HIV prevention treatment used to reduce the risk of HIV infection after a person has been exposed to the virus. It involves taking a combination of antiretroviral medicines for 28 consecutive days after a potential HIV exposure. PEP is intended for emergency situations only and is not a substitute for regular HIV prevention methods such as condoms or pre-exposure prophylaxis (PrEP). When started promptly and taken correctly, PEP can greatly reduce the likelihood of HIV infection. However, it must be started within 72 hours (3 days) after exposure, and the sooner it is started, the more effective it is. Ideally, PEP should be initiated within the first few hours after exposure.

How Does PEP Work?

 After HIV enters the body, it takes time for the virus to establish a permanent infection. During this early period, antiretroviral medicines can stop HIV from multiplying and spreading throughout the body. PEP works by preventing the virus from taking hold in the body’s immune cells. If treatment is started early enough and completed as prescribed, the body’s immune system can eliminate the virus before a permanent infection is established.

Because HIV begins to multiply quickly after exposure, every hour counts. Delaying treatment reduces the effectiveness of PEP, which is why anyone who believes they have been exposed to HIV should seek medical care immediately.

When Is PEP Recommended?

PEP may be recommended after situations where there is a significant risk of HIV exposure. A healthcare provider assesses each situation individually to determine whether PEP is appropriate.

Examples include:

• Unprotected vaginal or anal sex with someone known to have HIV or whose HIV status is unknown and who may be at high risk.
• Condom breakage or slippage during sex with a partner who is living with HIV or whose HIV status is unknown.
• Sexual assault or rape.
• Sharing needles, syringes, or other injecting equipment.
• Needle-stick injuries among healthcare workers.
• Accidental exposure of broken skin or mucous membranes (such as the eyes or mouth) to blood or body fluids that may contain HIV.
• Occupational exposures in healthcare or laboratory settings.

Not every exposure requires PEP. A healthcare provider will consider the type of exposure, the amount of body fluid involved, the HIV status of the source person (if known), and the time since the exposure occurred before recommending treatment.

When Is PEP Not Usually Recommended?

PEP is generally not recommended when:

• More than 72 hours have passed since the exposure.
• The exposure carries no realistic risk of HIV transmission.
• The source person is confirmed to be HIV-negative.
• The source person is living with HIV but has maintained an undetectable viral load, meaning they cannot sexually transmit HIV (U=U).
• The exposure involves body fluids that do not transmit HIV, such as tears, sweat, saliva (without blood), urine, or faeces.

Only a healthcare provider can determine whether PEP is necessary after assessing the individual situation.

The Importance of Starting PEP Early

The success of Post-Exposure Prophylaxis (PEP) depends largely on how quickly treatment is started after a possible exposure to HIV. HIV does not infect the entire body immediately after exposure. Instead, the virus first enters the body and begins to multiply locally before spreading to the immune system. PEP works during this early period by preventing HIV from establishing a permanent infection. Because of this, every hour matters. The sooner PEP is started, the greater the chance that the medicines will stop the virus before it takes hold. For this reason, healthcare providers recommend starting PEP as soon as possible, ideally within the first 2 hours after a high-risk exposure. However, PEP can still be effective if it is started within 72 hours (3 days) after exposure. After 72 hours, the virus may already have established infection in the body, and PEP is generally no longer recommended because it is unlikely to be effective.

Anyone who thinks they may have been exposed to HIV should not wait for symptoms to appear before seeking medical attention. HIV often causes no symptoms in the early stages, and by the time symptoms develop, it may be too late for PEP to work. Likewise, individuals should not delay treatment while trying to determine whether the exposure was serious enough or while waiting to speak to friends or family. Instead, they should go immediately to the nearest hospital, emergency department, HIV clinic, or health centre where a healthcare provider can assess the risk and decide whether PEP is appropriate. If the source person’s HIV status is unknown, healthcare providers can still perform a risk assessment and make a timely decision about starting treatment.

Delaying PEP significantly reduces its effectiveness because HIV continues to multiply and spread throughout the body with each passing hour. A delay of even one day may reduce the chances of preventing infection, and waiting beyond the 72-hour window usually means that PEP can no longer stop the virus from becoming established. This is why healthcare providers emphasize that PEP is a medical emergency rather than a treatment that can be postponed until it is convenient.

Starting PEP early must also be followed by taking every dose exactly as prescribed for the full 28-day course. Beginning treatment promptly but failing to complete the medication reduces its protective effect. In addition, follow-up clinic visits and repeat HIV testing are essential to confirm that the treatment has been successful and that HIV infection did not occur. Seeking immediate medical care after a potential exposure, starting PEP without delay, completing the full course of medication, and attending all follow-up appointments together provide the best chance of preventing HIV infection after a high-risk exposure.

The PEP Assessment

Before starting PEP, a healthcare provider performs an assessment to determine whether treatment is appropriate.

This usually includes:

• Asking about when and how the exposure occurred.
• Determining the HIV status of the source person if known.
• Assessing the level of HIV transmission risk.
• Reviewing the individual’s medical history.
• Asking about pregnancy where applicable.
• Reviewing current medications to avoid drug interactions.
• Performing an HIV test to confirm that the exposed person is HIV-negative before starting PEP.

Additional tests may include screening for hepatitis B, hepatitis C, sexually transmitted infections, and pregnancy, depending on the circumstances.

HIV Testing Before Starting PEP

An HIV test is performed before PEP is started whenever possible. This test establishes whether the person already has HIV before beginning treatment.

If the initial HIV test is positive, PEP is not appropriate, because the person already has HIV and requires lifelong antiretroviral therapy rather than emergency prevention treatment.

If the test is negative and the exposure is considered significant, PEP should be started immediately.

Completing the Full 28-Day Course

Completing the full 28-day course of Post-Exposure Prophylaxis (PEP) is essential for the treatment to provide the best possible protection against HIV infection. Once PEP has been started, the medicines should be taken every day for 28 consecutive days, exactly as prescribed by the healthcare provider. Although the medication begins working as soon as it is taken, it needs to remain in the body continuously throughout the treatment period to effectively prevent HIV from establishing a permanent infection. Missing doses, taking the medication irregularly, or stopping treatment before the 28 days are complete can reduce the effectiveness of PEP and increase the risk that HIV could establish infection if exposure has occurred. Some people may be tempted to stop taking the medication because they feel well or experience mild side effects such as nausea, headache, tiredness, or stomach discomfort.

 However, these side effects are usually temporary and often improve as the body adjusts to the medication. If side effects become bothersome, individuals should speak with their healthcare provider rather than stopping the medication on their own, as there are often ways to manage the symptoms or adjust treatment if necessary. Taking the medicine at the same time every day, setting reminders on a phone or alarm, using a pill organizer, or linking medication to a daily routine such as eating breakfast or brushing teeth can help improve adherence. Regular follow-up appointments during the 28-day period are also important, as healthcare providers monitor for side effects, provide counselling and support, answer questions, and ensure that the treatment is being taken correctly. After completing the full course, repeat HIV testing is carried out according to national guidelines to confirm that HIV infection did not occur. Completing every dose of PEP as prescribed gives the greatest chance of preventing HIV infection after a potential exposure.

Follow-Up After PEP

Starting PEP is only the beginning of care. Follow-up appointments are essential.

Healthcare providers usually:

• Check how well the medicines are being tolerated.
• Provide adherence support.
• Answer questions.
• Repeat HIV testing after completing PEP according to national guidelines.
• Screen for other sexually transmitted infections if necessary.
• Offer counselling on HIV prevention.

The timing of follow-up HIV tests depends on the testing method used and national recommendations, but testing is commonly repeated several weeks after exposure and again at the end of the recommended follow-up period to confirm that HIV infection did not occur.

What Should You Do While Taking PEP?

While completing the 28-day course, individuals are advised to reduce the risk of HIV transmission until follow-up testing confirms they remain HIV-negative.

Healthcare providers may recommend:

• Using condoms consistently during sex.
• Avoiding sharing needles or syringes.
• Not donating blood, organs, semen, or breast milk until advised it is safe.
• Attending all follow-up appointments.
• Taking every dose of medication on time.

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PEP Is Not the Same as PrEP

PEP and PrEP are often confused, but they serve different purposes.

Post-Exposure Prophylaxis (PEP)	Pre-Exposure Prophylaxis (PrEP)
Started after possible HIV exposure	Started before possible HIV exposure
Emergency treatment	Ongoing HIV prevention
Must begin within 72 hours	Taken before exposure occurs
Taken for 28 days only	Taken daily or as prescribed while a person remains at risk
Intended for unexpected exposures	Intended for people with ongoing or repeated risk of HIV exposure

People who frequently require PEP because of repeated HIV exposures should discuss PrEP with their healthcare provider, as it provides continuous protection and is more appropriate for ongoing risk.

Effectiveness of PEP

PEP is highly effective when:

• It is started as soon as possible after exposure.
• It begins within 72 hours.
• The medicines are taken exactly as prescribed.
• The full 28-day course is completed.

Although no prevention method is 100% effective, completing PEP correctly greatly reduces the risk of HIV infection after a significant exposure.