COVID immunology primer
Currently there are over 400 research companies working on a COVID-19 vaccine with around 24 in the clinical stages of testing. The clinical stage is where the product ( the vaccine) moves from the laboratory to testing in humans.
The important development stages that involve human subjects are stage 1 where a small number of patients are given the vaccine at different dosage levels and antibody response and adverse reactions are measured. Stage 2 involves testing a larger group of people looking mostly for tolerability and side effects. Stage 3 tests large groups of people for efficacy of the vaccine: whether it is protective of the groups of vaccinated patients compared to a group of unvaccinated patients against infection with the virus.
The multitude of vaccines are being developed with various methodologies.
A bit of immunology. There are 2 types of immune cells: B cells and T cells. B cells produce the antibodies that react with the virus and prevent it from invading cells (humoral immunity). Many different types of antibodies are produced after infection. The type of antibody most associated with protection from infection are called neutralizing antibodies which as their name would imply neutralize the detrimental effects of the virus on cells. and neutralizing antibodies. BLocing antibodies bind with a viral protein and make T cells recognize targets ( in this case cells with virus) and produce substances to destroy the cell and the virus (cellular immunity). Antibodies that are made may decline with time but there are memory b cells that when exposed to the same antigen viral proteins start producing new antibodies. T cells also produce memory cells that are activated upon reexposure to the virus. How long these types of immune responses last varies by disease states and is totally unknown with COVID 19. It is likely that the most successful vaccines will induce responses in both the T cell and B cell accesses.
Moderna in collaboration with the National Institutes of Health was one of the first companies to move into clinical trials. Its vaccine uses a piece of genetic material from the virus ( mrna) that is injected into humans, enters cells and programs them to produce an antibody to an important viral protein, in this case the spike protein. 45 volunteers who received 2 injections had produced neutralizing antibodies at the titres seen in patients who had recovered from COVID. This vaccine has been shown to produce a T cell response but weaker than its competitors. This vaccine is moving into phase 3 trial starting July 27.
Recent reports out of Oxford-AstraZeneca in a trial involving 1000 participants showed that an antibody and significant T cell response was evoked. This vaccine is made from a common cold virus ( adenovirus) that is modified and when injected into humans programs cells to make the coronavirus spike protein which then primes the immune system to attack the COVID virus should it enter the circulation.
The vaccine is made from a weakened form of a common cold virus, called an adenovirus, that's been genetically modified to carry instructions for cells to make the coronavirus's notorious spike protein. The idea is that, if the vaccine can instruct human cells to make this protein, the human system can learn to recognize it and better protect against infection.