Primary prevention means preventing illness before it occurs. Immunizations (vaccines) are one kind of primary prevention. Medicines that kill or control the organisms that cause infections are another type of primary prevention.
Secondary prevention means preventing a disease that a person has already had from coming back. This is usually done with medicines that slow or prevent the growth of the organisms that cause infections.
Generally, infection with HIV doesn't make people sick, except for the flu-like illness that may develop shortly after they become infected. Most people who are infected with HIV get sick because their immune systems become weak and cannot fight off other infections. So preventing opportunistic infections is an important part of treatment for HIV.
HIV infection comes in three stages. The first stage is called acute infection or seroconversion, and it typically happens within two to six weeks after exposure or becoming infected. This is when the body's immune system puts up a fight against HIV. The symptoms of acute infection look similar to those of other viral illnesses and are often compared to those of the flu. The symptoms may last a week or two and then completely go away as the virus goes into a non-symptomatic stage.