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Window Period

The "window period" is the time it takes for a person who has been infected with HIV to react to the virus by creating HIV antibodies. This is called seroconversion.

During the window period, people infected with HIV have no antibodies in their blood that can be detected by an HIV test, even though the person may already have high levels of HIV in their blood, sexual fluids, or breast milk.

Here is what the CDC says about the window period:

"Antibodies generally appear within three months after infection with HIV, but may take up to six months in some persons."

This CDC definition of a three to six month window period has been commonly used for a number of years.

What does this mean for you?

• The three month window period is normal for most of the population. Many people will have detectable antibodies in three or four weeks. Very, very rarely (i.e., only a few cases ever), a person could take six months to produce antibodies.
• You may be anxious to be tested soon after an encounter which you perceive to be risky (for a discussion of what behaviors put you at risk for HIV and which ones do not, see the section on How HIV Is Spread). You want to know: can I be antibody tested without waiting three months? How accurate is the test after, say, six weeks?
  
  Unfortunately, we simply don't know.
  
  Think about this: if you got a negative test at six weeks, would you believe it? Would it make you less anxious? If so, then go for it. But to be certain, you will need to be tested again at three months. Some test centers may recommend testing again at six months, just to be extra sure.

Although HIV may not be detected by a test during the window period, HIV can be transmitted during that time. In fact, individuals are often most infectious during this time (shortly after they have been exposed to HIV).