Worobey and his colleagues have started to map the subsequent spread of HIV-1 out from Kinshasa
to the rest of the world. The most common strain of HIV in the United States, for example, is known
as HIV-1 subtype B. The oldest lineages of HIV-1 subtype B are found in Haiti, and Worobey
estimates they branched off from African strains in the 1960s. That happens to be a time when many
Haitians who had been working in the Congo returned to their homeland after the country became
independent from Belgium. They may have unwittingly brought HIV back to the New World with
them. Haitian immigrants or American tourists may have then brought HIV to the United States. The
oldest lineages of HIV-1 subtype B in the United States, Worobey and his colleagues found, date back
to about 1970. That’s about four decades since the virus became established in humans, and about one
decade before five men in Los Angeles became sick with a strange form of pneumonia.
By the time scientists recognized HIV in 1983, in other words, the virus had already begun to turn
into a global catastrophe. As a result, HIV has had a huge head start on scientists who hope to halt its
spread. It would not be until the early 1990s that some strategies began to show real promise for
slowing the epidemic. Changing people’s behaviors has proven effective. Uganda launched a major
campaign against HIV that featured condom use and other public health measures. As a result, the
country reduced its HIV rate from about 15 percent in the early 1990s to about 5 percent in 2001.
Unfortunately funding for these programs began to ebb after a few years, and the infection rate in
Uganda has begun to rise again.
Other researchers have investigated medications that can slow the rise of HIV in infected people,
so that their immune systems can remain strong enough to block the onset of AIDS. Millions of people
now take a cocktail of drugs that interfere with the ability of HIV to infect immune cells and use them
to replicate. In affluent countries like the United States, these drug therapies have allowed some
people to enjoy a relatively healthy life. But the cost of these drugs has meant that most people with
HIV—living in the poorest countries—cannot afford a treatment that might give them extra years or
even decades of life. That’s beginning to change rapidly, as the United States and nongovernmental
organizations are now starting to provide these drugs to the most afflicted countries and as treatment
programs are starting to be scaled up dramatically.
Yet these drugs, even if they can prolong lives, are not the perfect cure. They have side effects that
can become harmful after years of therapy, and they foster the evolution of resistant viruses, which
then requires shifting patients to new drugs. In theory, the best solution to HIV would be a vaccine—
either one that could prevent people from becoming infected with the virus or one that could stimulate
the immune system of infected people to attack it effectively. Vaccines would be far less expensive
than treating HIV infection with drug cocktails and could help slow down the transmission cycle. But
the quest for an HIV vaccine has been a disappointing struggle so far. In 2008, for example, a highly
anticipated trial of a vaccine developed by Merck had to be abandoned because the vaccine appeared
to be making people more likely to acquire HIV, not less.
There’s good reason to worry about any HIV vaccine, even one that shows promise in small trials.
That’s because HIV is evolving in overdrive. HIV belongs to a group of viruses—including influenza
—that are very sloppy in their replication. They create many mutants in very little time. These mutants
provide the raw material for natural selection to act on, producing viruses that are better and better
adapted. Within a single host, natural selection can improve the ability of viruses to escape detection