The time it takes for HIV to affect the immune system varies in different people.

For example, the time it takes for the CD4 count to drop to 200 cells/mm³ can be longer or shorter.

Sometimes people who have very serious illness when they are first infected (during seroconversion) will lose CD4 cells more quickly.

There is no way to guess how quickly HIV will progress, other than by monitoring their CD4 count over time.

People who progress more quickly, and who lose CD4 cells more quickly, will still get as good and as strong a response to treatment, as people who progress more slowly.

Approximate time for CD4 count to drop to 200 cells/mm³

• 25% people take 1-2 years and (fast progressors)
• 50% people will take 2-10 years
• 25% people will take 10-15 years
• Less than 1% people will not see any drop in their CD4 count even after 15 years (long term slow progressors). Even more rarely, a few people not only keep a strong CD4 count, but they also keep an undetectable viral load. Viral load is discussed in the next chapter.

These results are based on a UK study of people who were diagnosed during seroconversion. They were then followed over time to see how their CD4 count changed. This may overestimate how quickly HIV progresses as people are often diagnosed early because of symptoms. But it may underestimate the the time until someone needs to start treatment as this was based on the older recommendation to start treatment at a CD4 count of 200.

Link to UK Seroconvertors Study.

Time between infection and the need to start treatment

A study in the UK that follows people diagnosed within six months of infections reports that:

• 25% of people start treatment within 2 years of infection.
• 50% start between 2 and 10 years after infection.
• 25% have not started after 10 years.

This range of responses is important to know.

It is especially important when speaking to people who are recently diagnosed.