“Drug holidays” or structured treatment interruptions (STI)
Antiretroviral therapy improves the health of persons with HIV by suppressing the virus and thus slowing the progression of the disease to Aids. On the other hand, the drugs have side-effects, are expensive and many people find it difficult to take them for long periods without any breaks.

A few years back, some scientists came to think that it might in fact be a good thing to have breaks from antiretroviral treatment, in order to stimulate the body’s immune response to HIV. When HIV is suppressed to very low levels in the blood for long periods (as occurs with antiretroviral therapy), a person might lose their natural immune response to the virus. The immune system is very important in controlling the virus, along with antiretroviral treatment.

If treatment is stopped, the virus quickly multiplies and levels in the blood rise. This could serve to switch on and strengthen the immune response, in a process that has been called “autovaccination”. A small number of scientific studies with people on antiretroviral treatment set out to study what would happen if there were controlled, short treatment breaks, called structured treatment interruptions, or “drug holidays”.

These studies have shown that there is measurable, increased recognition of the HI virus by the immune system following treatment breaks. However, these effects on the immune system are similar to what is found in people before treatment, and do not seem to have long-term benefits in people with established HIV infection. (There may be more benefit in people who started antiretroviral treatment very soon after they were infected with HIV.)

Another concern is that there is evidence that drug resistance is more likely to occur following structured treatment interruptions, just as it is more likely to occur when people interrupt their treatment for other reasons.

Because at this stage there is no clear answer as to whether structured treatment interruptions is a good thing and also uncertainty about how often and how long interruptions should be, structured treatment interruptions is not advised for any person on antiretroviral treatment except as part of a properly controlled and monitored scientific study. Many scientists now believe that it is probably safer to use other ways to stimulate an immune response to HIV in patients on treatment. Such methods could include cytokines (immune messenger molecules) or HIV vaccines.