There are two main types of vaccines:
Preventive Vaccines
A preventive vaccine is given to people who don’t have an illness and teaches the body to prevent that particular illness or prevent it from developing into 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 organisms like viruses that cause disease.) If the foreign invader enters the body after vaccination, the immune system may recognize it because of the vaccine, and can react quicker and block it (like with the measles vaccine), or control it so that it does less damage (like with seasonal flu vaccines).
Therapeutic Vaccines
Therapeutic vaccines may slow down the rate of progression of HIV when the virus is already in the body, or perhaps 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. Since we don’t have an approved therapeutic vaccine yet, it is hard to know exactly how a future therapeutic vaccine will work.
Ways Scientists Believe a Preventive Vaccine Could Work
Trigger Antibodies
A vaccine might prevent infection completely by triggering a strong antibody response. This is how the measles vaccine works.
Trigger T-cell Response
A vaccine might trigger a strong T-cell response to combat an infection and clear it from the body to prevent it from developing into disease. This helps people not get as sick and avoid hospitalization, and helping people recover more quickly.
Slow Down Disease Progression
A third approach is to slow down the virus, making the time from getting HIV to developing AIDS stretch out even longer by helping people to control their viral load. Also, people with a lower viral load are less likely to transmit HIV to others.
Community Immunity (also called Herd Immunity)
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 very young children and people with certain other medical conditions.
Combining Vaccines
Perhaps one vaccine will not be enough to trigger the right combination of immune responses, and we will need a combination of products to prevent HIV, similar to combination antiretroviral therapy used to treat people who are living with 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. Then one or more different vaccines are given in a series over time to “boost” the immune response. Several studies currently underway are looking at various prime-boost combinations.
Adjuvants to Boost Vaccines
Adjuvants are products added to a vaccine to increase or strengthen the immune response. You can think of them as a power booster, or 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 fewer 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.