In the race for a vaccine to end the global COVID-19 pandemic, eight contenders are at the front of the pack.
These eight vaccine candidates are undergoing human testing in clinics in China, the United States, Britain and Germany. Behind them are at least 94 others in various stages of development.
The eight vaccine candidates fall into three categories.
One category might be called the classical technique: triggering the patient’s immune system to respond to the virus by injecting a killed version of it. Three separate groups of Chinese researchers are testing inactivated-virus vaccines.
A second method uses one virus to fight another.
Whether it causes COVID-19, Ebola disease or the common cold, a virus is basically just an envelope containing instructions to make more of the virus.
In this novel vaccine strategy, scientists strip out instructions from one virus and replace them with instructions to make just a piece of the coronavirus.
A shot of the modified virus does not cause illness. The virus infects some of the patient’s cells, but instead of copies of infectious virus, those cells produce the piece of coronavirus. The patient’s immune system responds to the coronavirus protein so it can fight off the invader later.
Two separate groups from China and Britain are pursuing this approach.
A third novel strategy cuts out the middleman. Rather than delivering instructions in a virus, researchers inject genetic code for a piece of the coronavirus directly into the patient in the form of DNA or RNA.
Two groups are working on RNA vaccines, and one on a DNA shot.
The newer methods are fast and flexible.
Each technique has pros and cons.
The killed-virus system is the most tried-and-true. But killing the virus can change its shape. The immune system might respond to the killed virus differently than the real thing.
Viral vectors are a new strategy, and it’s not clear how well different carrier viruses will work. In some cases, people may have already been exposed to the carrier virus, which would reduce its effectiveness.
Experts are concerned that the extremely compressed timeline will not allow for definitive answers on whether a vaccine is safe and effective.
Developing a vaccine typically takes around 20 years. It’s usually tested in tens of thousands of people before it’s approved for wider distribution, because safety issues may not be immediately obvious.
For example, in a clinical trial of 35,000 patients, researchers discovered that a dengue vaccine did more harm than good for children under 9 years old who had not had a case of dengue before receiving the vaccine. They developed more serious cases of dengue than those who had not been vaccinated before their first dengue infection.
