A preventive vaccine is given to people who don’t have an infection and teaches the body to prevent a particular infection or fight a disease. The vaccine does that by teaching your immune system to recognize and fight a foreign invader (like HIV) if it enters the body. (Your immune system helps you fight off infections.) If the foreign invader enters the body after vaccination, the immune system can react quicker and stop the infection, or control it so that it does less damage.
Therapeutic vaccines may slow down the rate of progression of HIV when the virus is already in the body or help to control viral load. This means that a person may not progress to AIDS as quickly, and they may be less likely to transmit HIV to others as a result of the vaccine. It is also possible that a therapeutic vaccine could work together with someone’s antiretroviral medications to control HIV, perhaps enabling a person to use fewer medications or a lower dose.”
A vaccine might prevent infection completely by triggering a strong antibody response
A vaccine might trigger a strong T-cell response to combat an infection and clear it from the body to prevent disease. This is the way we are able to fight back against a cold or the flu.
A third approach is to slow down the infection, making the time from getting HIV to developing AIDS stretch out even longer by helping to control viral load. Also, people with a lower viral load are less likely to transmit their infection to others.
A vaccine may also benefit the wider public, even those who are not vaccinated. This idea is called community immunity or herd immunity: if enough people get vaccinated, making those people less likely to transmit HIV to others, then the wider community will have some protection as a result. This can help protect people who are unable to be vaccinated, such as children or people with other medical conditions.
Perhaps one vaccine will not be enough to trigger the right combination of immune responses, and we will need a combination of products to attack the virus, similar to combination therapy used to treat people who are living wiht HIV.
In this scenario, one vaccine is given to get the immune system ready for action, or “prime” it. Priming may require more than one dose. One or more different vaccines are given at the same time or at later time points to “boost” the immune response. Several studies currently underway are looking at various prime-boost combinations.
Adjuvants are products added to a vaccine to increase the immune response. You can think of them like a power booster, like adding hot sauce to your food for extra flavor.
Researchers think it is possible that if we could find a good, powerful adjuvant, it might be possible to give a smaller dose of vaccine, or perhaps a smaller number of injections. Additionally, sometimes adjuvants are needed for a vaccine that can’t induce a strong enough immune response on its own. The HVTN often tests new experimental adjuvants in our studies.