Unbeknownst to many people, there are multiple strains of HIV. The more aggressive HIV-1 strain is found worldwide, while HIV-2 is found mainly in West Africa, though pockets of cases have been found in Europe, India, Japan, and the United States. A team of researchers hailing from Sweden’s Lund University has found that people who are infected with the HIV-2 strain, followed by HIV-1, seem to better equipped at fighting the disease.

The study followed 4,700 people in the African country of Guinea-Bissau over the course of 20 years, and focused on 223 people who first had the HIV-2 virus and were later infected with HIV-1 compared to individuals who had only been infected with the HIV-1 strain.

Researchers now wonder what the factor that accounts for the difference is. Is there something in the HIV-2 virus that is less damaging to the human body’s immune defenses? Or does the explanation lie in the human body itself?

Researchers were astonished to find that in people who had contracted only the HIV-1 strain their condition developed into full-blown AIDS in, on average, under six years, or 68 months. But for people who contracted HIV-2, followed by HIV-1, their condition deteriorated into AIDS in an average of nine years, or 104 months – or 50 percent longer than their counterparts with just HIV-1.

Scientists have known for a while that different genetic varieties of HIV exist when it is contracted; the less genetic variety, the closer that patient is to AIDS. Researchers also studied study participants’ T cells – cells in the immune system that the HIV virus attacks. According to the abstract for the study,

CD4+ T-cell levels were higher and CD8+ T-cell levels increased at a lower rate among participants with dual infection, reflecting slower disease progression. Participants with dual infection with HIV-2 infection preceding HIV-1 infection had the longest time to AIDS and highest levels of CD4+ T-cell counts. HIV-1 genetic diversity was significantly lower in participants with dual infections than in those with HIV-1 infection alone at similar time points after infection.

Scientists are hopeful that “these findings could have implications for the development of HIV-1 vaccines and therapeutics.”

Researchers are careful to stress that people infected with HIV-1 should not by any means seek out the HIV-2 strain.

The results of the study have been published in the New England Journal of Medicine.

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