FACTSHEET

A

Adenovirus: This is a common virus that causes colds and sore throats. A defective adenovirus (one that cannot grow or cause adenovirus infections in humans), such as Ad26, is sometimes used as a viral vector in HIV vaccines.

Active immunization: This is what takes place when a vaccine stimulates the body to produce an immune response, such as the production of antibodies. Active immune response takes days or weeks to develop but may be long lasting – even lifelong. See also Passive immunization.

Adjuvant: This is an ingredient included with the vaccine to boost the immune response.

Amino acids: These are molecules that link together in combinations to form proteins.

Animal models: Research workers often use laboratory animals as models of humans to test medicinal products they want to develop. The safety of drugs and vaccine candidates are studied in animals at the pre-clinical stage of research. Such testing is a legal requirement before tests on human volunteers can take place in clinical trials.

Antibodies: These are protein molecules produced by the immune system to disable or destroy harmful pathogens (for example, bacteria and viruses).

Antigen: Any substance that causes the body to make an immune response against it is an antigen. Antigens include viruses, bacteria, toxins, chemicals or other substances that usually come from outside the body.

B

Broadly neutralizing antibodies (bNAbs): These antibodies can protect the body from a wide range of different types of HIV. bNAbs are passively administered candidates in HIV prevention studies; researchers are also exploring how to induce bNAbs with a vaccine.

C

Clade: A clade describes a family or strains or sub-types of HIV descended from the same origin.

D

DNA vaccine (nucleic acid vaccine): This is a direct injection of genetic material that contains the instructions for making specific antigenic protein(s), resulting in direct production of such antigen(s) within the vaccine recipient in order to trigger an active immune response against the antigen (see active immunization).

E

Efficacy: This is a measure of how effective a drug or vaccine is in the context of a clinical trial. Drugs and vaccines can show high efficacy within research studies, but not be very effective in the real world due to issues such as compliance with the vaccine regimen. A vaccine that requires multiple injections to prevent HIV infection may not be as effective if all injections are not received.

Envelope protein trimer (gp140): This protein on the surface of HIV binds to immune system cells to gain entry into them, allowing HIV to multiply and spread. The envelope is made up of identical units linked together in groups of three; hence the name, trimer. HIV’s high rate of mutation allows it to change the structure of the trimer and enables evasion by the immune system. Antibodies that target HIV recognize structures (epitopes) on the HIV trimer, while trimer-binding neutralizing antibodies block HIV from infecting cells. Trimers have been engineered synthetically and are now being tested as vaccine candidates that induce active immunity.

Epitope: An epitope is the part of an antigen that is recognized by and binds to components of the immune system, such as antibodies or immune system cells.

F

First in human: This term is used to describe the first time a vaccine or drug has been given to humans.

Follow-up: This describes the monitoring of a person’s health over time after the intervention has been administered. It includes keeping track of the health of people who participate in a clinical study or clinical trial for a period of time, both during the study and after the interventions are completed.

Formulation: This is the way different components are combined to make a vaccine or medicine.

H

HIV proteins: The mature, infectious HIV has five structural proteins. Harmless synthetic versions of these are used in many vaccine approaches and tests for infection.

M

Monoclonal antibodies (mAbs): These antibodies are produced by identical immune cells that are all clones of a unique parent cell. Broadly neutralizing antibodies (bnAbs) are mAbs that bind diverse and neutralize multiple HIV strains, despite their differences.

P

Passive immunization: This refers to pre-formed antibodies administered passively to protect against infection. Current formulations are likely to give immediate, but short-lived protection – several weeks to three to four months at most – so needs to be repeated. See also Active immunization.

Pathogen: A pathogen is an organism (for example, a bacteria or virus) that has the potential to cause disease.

Phase 1 clinical trial: This is a safety study that involves giving the vaccine to a small group of people (up to 100) to ensure there is no harm and to see if it provokes an immune response.

Phase 2 clinical trial: This is a larger safety study with hundreds of people to learn more about safety in diverse populations, the most appropriate dosage and to expand knowledge of the vaccine’s immunogenicity.

Phase 2b clinical trial: This is a “proof-of-concept” study to see if there is value in taking a candidate further before committing to a much larger and more costly Phase 3 study to establish efficacy. The number of volunteers required is smaller, around 2,000 to 5,000, while more than 10,000 volunteers are required for Phase 3 trials.

Phase 3 clinical trial: This is a final study where the vaccine is compared against a placebo to measure how effective it is at preventing infection (known as efficacy). These studies enrol thousands of people and can detect rarer side-effects, as well as identify the best dosage levels. Phase 3 trials are required before new vaccines can be licensed for use.

Pre-clinical study: This term refers to research undertaken before vaccines can be tested in humans.

PrEP: This acronym stands for pre-exposure prophylaxis. It is a pill or tablet taken daily or peri-coitally (before and after sex) by HIV-negative people that reduces the risk of getting HIV.

Prime boost: This is a combination strategy whereby the immune system is “primed” or triggered by one vaccine component and then a different element targeting another part of the immune system provides a “boost”.

Protein-based vaccine: This vaccine is made up of a protein antigen designed to trigger an active immune response.

T

Trimer: See Envelope protein trimer (gp140)

V

Vaccine candidates: These are potential vaccines being tested in clinical trials.

Viral vector: This virus does not cause disease in humans and is used as a vehicle to transport vaccine ingredients into the body.