Developing a vaccine is a complicated process, but the fundamental idea behind a vaccine is straight-forward. Vaccines train the immune system to recognize and combat pathogens (viruses or bacteria). A vaccine basically simulates the pathogen (in our case the SARS CoV-2 virus) by introducing an antigen specific to the target virus.
That triggers an immune response and the body forms antibodies and killer T cells to fight what it believes is the invading virus (and remembers them for the future). If the person is later exposed to the virus, the immune system will recognize the antigens immediately and attack aggressively before the pathogen can spread and cause sickness.
The key to vaccines is injecting the antigens into the body without causing the person to get sick. Scientists have developed several ways of doing this, and each approach makes for a different type of vaccine.
Recombinant Vaccines
A recombinant vaccine is a vaccine produced via DNA technology. This involves inserting the DNA encoding an antigen (such as a bacterial surface protein) that stimulates an immune response expressing the antigen in cells.
The University of Oxford and AstraZeneca vaccine uses a recombinant vaccine. A chimpanzee adenovirus carries a DNA code the for the SARS CoV-2 spike antigen into cells. The body then mounts an immune response to the SARS antigen. This vaccine is in Phase III trials with about 50,000 participants (but they’re starting with 10,000).
m-RNA Vaccines
This is a new approach to making a vaccine. Moderna and Pfizer are using this new approach. They deliver nano-particle mRNA genetic sequence into host cells which tells the cell to replicate the SARS CoV-2 virus protein coat, triggering the immune response.
Both these manufacturers are just beginning their Phase III trials. The Moderna’s Phase III trial will have 30,000 participants in the US. Arizona is a participating trial location. Pfizer’s will also be 30,000 persons but will be in 3 different countries.
Inactivated Vaccines
For these vaccines, the specific virus or bacteria are killed with heat or chemicals, and the dead cells are introduced into the body. Even though the pathogen is dead, the immune system can still learn from its antigens how to fight live versions of it in the future.
A few companies are also focusing on whole-virus weakened or killed SARS-CoV-2 virus. The Sinovac vaccine uses this approach. It’s in Phase III trials with 9,000 healthcare workers in Brazil.
Subunit/conjugate Vaccines
For some diseases like SARS CoV-2, scientists can isolate a specific protein or carbohydrate from the pathogen that can train the immune system to react without provoking sickness.
Sanofi and GlaxoSmithKline are working together on a vaccine that uses this protein subunit approach. Their lead vaccine candidate consists of the spike antigen combined with an adjuvant.
Live Attenuated Vaccines
For these types of vaccines, a weaker, asymptomatic form of the virus or bacteria is introduced into the body. Because it’s weakened, the pathogen won’t cause sickness, but the immune system will still learn to recognize its antigens and know to fight in the future.