How Vaccines Work

Man receiving shot


Preventive and therapeutic vaccines

There are 2 main types of vaccines. A preventive vaccine is given to people who are uninfected 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 slow down the rate of progression of HIV infection when the virus is already in the body. This means that a person may not progress to AIDS as quickly, and they may be less likely to infect others as a result of the vaccine.

Using lab-made parts of HIV

In general, preventive HIV study vaccines are made in the lab to look like parts of HIV. They are designed to cause a response in your immune system. Because we only use parts made in the lab to look like the real virus, [c1] , we can confidently say it is not possible to get infected with HIV from the study vaccines.

In recent years, other groups have done small studies in people already infected with HIV using a vaccine made from the virus itself. These studies are separate from what is discussed here, and only apply to people who already have HIV infection.

Inserts and adjuvants

An insert is a piece of genetic code that tells the body to make some proteins found in HIV. Proteins are natural substances. They help build and maintain your body, and do the same for viruses such as HIV. You can learn more about how inserts are used in Types of Vaccines.

A vaccine may also include an adjuvant. Adjuvants are products used to boost the body’s reaction to the vaccine. Many licensed vaccines (against other diseases) use adjuvants. Some examples:

  • GM-CSF is used in cancer treatment. It causes the body to build more white blood cells. The HVTN has tested vaccines containing GM-CSF in several studies.
  • MF-59 is commonly used in licensed vaccines in Europe (for example in flu vaccines). The HVTN has also tested vaccines containing MF-59 in several studies.

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 even 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.

Preventing or controlling infection

There are several possible ways that scientists believe a preventive vaccine could work:

  • 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 initial HIV infection 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 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.

More than one vaccine?

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 HIV-infected).

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), and 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.