Although they measure different things, the pattern of viral load and CD4 results are usually related.

• Generally when viral load is low, CD4 counts will be high.
• Likewise, when CD4 counts are low, viral load will be high.

A few weeks after infection when HIV levels go up to very high levels, CD4 counts drop.

Then as the immune system brings viral load levels down, CD4 counts go back up again.

There is sometimes a lag between viral load and CD4 changes:

• After starting treatment viral load drops very quickly, but CD4 counts sometimes take several months before they start to increase
• If treatment fails and the viral load level start to rebound, the CD4 count may still continue to rise for a while.
• As viral load gets higher, the CD4 count will nearly always start to fall within a few weeks.

You can now see how the CD4 count and viral load curves fit together.

CD4 count and viral load without ARV treatment

After infection, viral load levels are very high, but then your body fights back and it drops to much lower levels. Over time though, usually over several years, the level of virus increases again. The level of virus in the body continues to rise and the CD4 count continues to fall.

When the CD4 count is very low, the immune system is no longer strong enough to fight off opportunistic infections. This causes serious illness. Some of these infections can be fatal.

Without treatment, HIV infection is fatal.

Effect of ARVs on CD4 count and viral load

After infection, viral load levels are very high, but then your body fights back and it drops to much lower levels. Over time though, usually over several years, the levels of virus increase again. It is usually high (around 50,000-100,000 copies/mL) by the time that your CD4 count drops to around 350 cells/mm³.

After starting treatment, viral load falls quickly and CD4 counts rise slowly.

If ARV treatment brings viral load down to less than 50 copies/mL, then treatment can last for many years.