A new pre-publication study released April 19 from Sinovac Biotech demonstrates that their COVID-19 vaccine is effective at protecting monkeys from coronavirus. Macaque monkeys received three injection of a novel vaccine at medium or high dosage, and were compared to control monkeys that received a placebo vaccine. These monkeys were then exposed to COVID-19 after 22 days. Monkeys that received the vaccine showed almost no signs of the virus, while the control monkeys developed the severe pneumonia and other coronavirus symptoms.
Vaccines operate by training the immune system to recognize a disease-causing agent, so that immune system will be equipped to defend against the invader if it infects the body. The body naturally develops antibodies to foreign agents it encounters, so a vaccine aims to introduce a harmless version of a virus to a person, allowing the immune system to develop the appropriate antibodies.
There are several ways vaccines operate to achieve immunization. A modern approach to vaccines uses only a piece of the virus, since the body doesn’t need to recognize the entire virus to develop an immune response. Vaccines of this nature can be easier to mass produce, since the proteins used in the vaccine can be expressed in a fast-growing cell culture. The challenge is developing a cell line that is able to produce the protein in the exact form seen in the virus so that the vaccine is actually effective.
This study uses a more traditional approach — producing copies of the COVID-19 virus, then inactivating them, before formulating the inactivated virus into a vaccine. Inactivated virus vaccines require less knowledge about the virus and its proteins, which is a major advantage when working with a novel infectious disease. Sometimes there are challenges in mass production, as inactivated virus vaccines usually require animal cell cultures, which can be difficult to work with. There are also concerns that the viral particles may not be sufficiently inactivated, and may cause an infection in a percentage of the individual who is supposed to be immunized.
The Sinovac vaccine did not appear to cause infection in any of the monkeys that were tested, even when they were given a high dosage. There is also a danger that untested vaccines can cause the immune system to become overstimulated, leading to what is called a “cytokine storm”. The Sinovac vaccine did not appear to cause adverse immune system reactions. In fact, the monkeys appeared to be completely healthy and content, which suggests the vaccine may be safe for humans.
As is always the case with animal trials, there is no guarantee that this vaccine will be effective in humans. Human trails are already underway according to reports. Even if this vaccine is effective in clinical testing, it will take months to scale up production. With that said, it is exciting that there is a strong candidate for a vaccine.
This is part of a series covering new research that relates to the COVID-19 pandemic. COVID-19 medicine is evolving rapidly, and some of the science discussed here could end up being incorrect.