Currently there are over 400 research companies working on a COVID-19 vaccine with around 24 that have advanced to the clinical stages of testing. This is the stage is where the product ( the vaccine) moves from development in the laboratory to testing in humans.
The important clinical testing 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 works to protect a the group of vaccinated patients against the viral infection compared to a group of unvaccinated patients. The multitude of vaccines are being developed using a variety of methodologies.
COVID immunology primer
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 antibodies 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. Immune T cells are also activated in an immune response. They bind with a viral protein and make T cells recognize targets ( in this case cells with virus) and in addition they can produce substances to destroy the cell and the virus (cellular immunity). Antibodies that are made acutely may decline with time but the immune system also produces memory B cells that when exposed to viral proteins that they recognize start producing new antibodies. T cells also produce memory cells that are activated upon re exposure 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 cells and B cells.
Three vaccines in development have recently made the news.
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 produced neutralizing antibodies at the titers 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 released from the collaboration of Oxford University and AstraZeneca are also promising. In a trial involving 1000 participants significant antibody titers and a 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 is then recognized by the body which then produce antibodies and a T cell response against the virus.
On July 22, 2020 the White House announced a $2 billion dollar contract given to Pfizer in collaboration with the German company BioNTech. This collaboration is working on a vaccine that has recently shown promising phase 1/2 data . This is also an mRNA based vaccine that uses fragments from the virus injected into cells. Sixty patients have been studied so far at different dosage levels with robust antibody and T cell responses being shown. The contract is for the development and distribution of 600 million doses of vaccine if phase 3 trials prove safety and efficacy.
These three are among the first of many vaccines in development. The future certainly seems hopeful for a successful COVID vaccine.