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Why can HIV infection have few symptoms for many years?

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AIDS Scanning electron micrograph of HIV-1 virions (green) budding from a cultured lymphocyte. Multiple round bumps on the cell surface represent sites of virion assembly and budding.

Following the initial acute phase of infection, HIV enters a prolonged period known as clinical latency or the asymptomatic phase, which can last an average of 10 years. During this time, the virus remains active and continues to replicate, but it does not cause significant symptoms.123

The lack of symptoms during this stage occurs because the virus is slowly and steadily depleting the body's helper T cells (CD4+ cells) without immediately compromising the overall function of the immune system to a critical degree. Because the immune system is still able to manage other pathogens during this period, the individual typically feels healthy.123

However, as the CD4 count gradually declines, the immune system becomes increasingly vulnerable. Once the count falls to approximately 200 cells per microlitre of blood, the body loses its ability to fight off opportunistic infections and malignancies, marking the progression to AIDS.132