The HIV window period also called the HIV incubation period or the seroconversion is the period, which exists between the time you get infected with HIV (human immunodeficiency virus) and the time your blood test takes to detect the antibodies to the virus and show a positive result.

Why is there a window period?

The reason why this window period exists is that the most commonly used tests to detect HIV do not look for the virus. Instead, they look for the antibodies that the body produces to fight the human immunodeficiency virus.

After infection, the body’s immune system takes time to develop antibodies to fight the virus. The standard screening tests show their results by detecting the antibodies to the virus in the blood.

The HIV tests cannot reliably detect the infection until after the detectable levels of antibodies are available in the blood and the window period has passed.

Testing guidelines, therefore, allow for repeat testing during the following weeks and even months in negative reports to rule out a false negative result.

The next post describes the various tests used to diagnose HIV infection along with the accuracy and the window period.

Can a person be infectious during the window period?

A person who has been infected with HIV can pass on the infection to others during the window period. As a matter of fact, the infected person is most infectious during the initial weeks of getting infected.

It is during this initial untreated primary infection stage, that the person has an exceptionally high viral load.

There is conclusive evidence that an infected person is more likely to pass on the infection to another during the window period. This is because he does not know that he is infected and carries on his sexual exploits unabated. During the window period, his blood test also shows a negative result.

Therefore, if you have had a doubtful sexual exposure, you must test yourself keeping in mind the window period duration. Even infection with one sexual encounter is possible. 

If your test comes negative, you must follow up testing for the full duration that the window period requires to rule out the HIV infection.

Follow-up testing is often done 6 weeks, 3 months, and even 6 months post-exposure to rule out the HIV infection.

During the window period, the infected individual will exhibit symptoms of the disease, which are similar to those of flu or cold. They do not raise any suspicion of the deadly infection lurking in the blood and which is not showing up in blood tests. This is what makes HIV a dangerous disease to the community and why it has become a global epidemic.

Once diagnosed as a positive case, the person is put on treatment with antiretroviral therapy (ART), taking care to manage the side effects of antiviral drugs, and monitoring the patient’s response to ART. 

According to the CDC

The Centers for Disease Control and Prevention (CDC) reports that in an average person, antibodies start to develop in the blood within 25 days after the person gets infected with HIV. And the production of detectable levels of antibodies takes time (which is the window period).

For example, if you have sex on Monday and get infected and test yourself on Tuesday, your test will come negative. Even if you test after one month, the test may still come negative – falsely.

A proper testing procedure must be followed and testing should be done after the window period has elapsed to celebrate that you are not HIV positive.

This window period varies from disease to disease, from person to person, and from test to test.

For HIV antibodies to show up in the blood and get detected by laboratory tests, the time varies from three weeks to six months.

The window period also differs from test to test, as some tests are more sensitive than others.

In some cases, the antibodies may get detected one month after getting infected. But in most people (97% of the cases), the lab tests show a correct positive result within three months after the person has been infected.

Rarely, the window period may be prolonged and the tests will react positive, correctly, only after six months. And, it is still very rare and unlikely that the window period will prolong more than six months.

CDC guidelines

The Centers for Disease Control and Prevention (CDC) offers both a 3-month and 6-month guideline.

The 3-month guideline is for the population at large.

The 6-month guideline is for those

  • receiving chemotherapy
  • under Hepatitis C treatment
  • receiving PrEP or PEP treatment
  • diagnosed with a pre-existing immunodeficiency disorder, such as for example, Crohn’s disease.

Those who fall into any of these 4 categories must get tested at the 6-month period since these conditions can disturb the accuracy of an HIV test result at the 3-month mark.

However, today, with sensitive HIV tests, most antibodies to the virus can be detected within three weeks.

According to WHO guidelines

WHO is changing its recommendation towards a 6-week window period of HIV for conclusive results instead of 12 weeks.

Since HIV tests are constantly improving and being modified, the 12-week guideline is likely to change in the future — both with WHO and the CDC.

In fact, a consensus is evolving among many HIV specialists that the 4th generation antigen/antibody test, a test that is now increasingly being used for HIV diagnosis, is conclusive after 6 weeks – meaning that the window period for the 4th generation test is 6 weeks.

The CDC too, states that it can take 2 to 6 weeks, which is the window period for the infected person’s body to make enough antigens and antibodies for a combination 4th generation test to detect HIV.