How Does China’s CoronaVac Vaccine for COVID-19 Work?

By Nidhi Parekh of The Shared Microscope

The international race to a viable COVID-19 vaccine is ongoing, including in China, where COVID-19 infections first broke out. Chinese biotech company Sinovac has developed a vaccine called CoronaVac. This vaccine is made from an inactivated version of the virus that causes COVID-19 (called SARS-CoV-2). Read on to learn more about how CoronaVac works in detail.

Check out other posts in our COVID-19 vaccine series:
[Moderna | Oxford/AstraZeneca | Pfizer/BioNTech | Johnson & Johnson | Novavax | Sinovac]

Table of Contents:

Chinese Biotech Companies Are Major Players in the COVID-19 Vaccine Race

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Research has been underway in China since the early days of the COVID-19 crisis. The race to a vaccine got a good start in January 2020, when China published the genetic sequence for SARS-CoV-2, the virus that causes COVID-19.  Since then, dozens of laboratories around the world are now the battlegrounds in the race to develop a COVID-19 vaccine.

China is a leader in the race to a vaccine, with the most number of COVID-19 vaccines currently in human trials. By June 2020, six Chinese companies had introduced COVID-19 vaccine candidates in human trials.

Sinovac’s CoronaVac Vaccine

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The most promising of the Chinese COVID-19 vaccines currently in human trials is CoronaVac.  CoronaVac is under development by a Beijing-based pharmaceutical company called Sinovac Biotech. The company has developed human vaccines for conditions such as hepatitis A and B, and has also led efforts to develop vaccines for avian flu and swine flu.

The most promising Chinese #COVID19 vaccine that is currently in human trials is CoronaVac, which is from Beijing-based biotech company Sinovac.

Currently in Phase 3 trials in Brazil, Sinovac’s CoronaVac vaccine is a frontrunner in the race to develop a COVID-19 vaccine.  Sinovac’s ambitious goal is to have CoronaVac ready for the market by late 2020, but, of course, approval for patient use hinges on successful completion of the trials.  

CoronaVac, Moderna, Oxford: Three Different Vaccines, One Goal

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Others leading the way in this international race to a vaccine for the novel coronavirus are the United Kingdom’s Oxford/AstraZeneca vaccine and the United States’ Moderna vaccine. 

What’s interesting to note is the top three vaccines are all different types. The Oxford/AstraZeneca vaccine uses viral vectors, and the Moderna vaccine uses mRNA.  By contrast, CoronaVac uses an inactivated version of the SARS-CoV-2 virus itself.

Furthermore, Oxford and Moderna have something in common with each other that they do not have in common with CoronaVac.  The methods used by both Oxford and Moderna rely on the latest tools of modern biology to foster immunity to a small part of the SARS-CoV-2 virus that causes COVID-19.  In both the Moderna and Oxford vaccines, the human body develops immunity to a small part of the SARS-CoV-2 virus — the spike protein, a part of the SARS-CoV-2 molecule which mediates viral infection.

By contrast, CoronaVac uses the whole, inactivated virus — not just the spike protein — as the basis of the vaccine.  CoronaVac uses an age-old method of growing the SARS-CoV-2 virus in bulk, and then inactivating it using chemicals. The method used by CoronaVac has been used consistently throughout history, with the polio vaccine being the most notable of them all.

What is an Inactivated Vaccine?

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Inactivated vaccines are made by inactivating, or killing, the pathogens (that is, bacteria or viruses) during the process of vaccine development. Heat or chemicals such as formaldehyde are used to inactivate viruses for use in vaccines. The main benefit of inactivated viruses — and the reason why they are used in vaccines — is that they exhibit the whole virus to the immune system, and because they are killed, cannot cause disease.

The inactivated vaccine is the first type of vaccine that was ever invented. The history of vaccines, and of inactivated vaccines, in particular, goes back to the late 18th century, when an English doctor named Edward Jenner, who is widely known as the father of immunology, developed a vaccine for smallpox. Jenner’s smallpox vaccine helped eliminate a very serious disease that “devastated mankind for centuries,” as Dr. Stefan Riedel writes. Thanks to this vaccine, smallpox was eradicated in 1980.

English doctor Edward Jenner, widely known as the father of immunology, invented the first inactivated #vaccine in the late 18th century — the smallpox vaccine. @TheSharedScope

inactivated vaccine

Scientists are working on many forms of COVID-19 vaccines, including an inactivated virus version such as in CoronaVac.  Other types of vaccines in development include mRNA vaccines, viral vector vaccines, and protein based vaccines.  Source: The Shared Microscope on Instagram.

 How Do Inactivated Vaccines Work?

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Inactivated vaccines work because they cannot cause disease — they have been treated with heat or chemicals to render them unable to actively cause disease in the body.  However, once an inactivated vaccine is injected into the body, the immune cells in our bodies will recognize the inactivated pathogens (in CoronaVac’s case, the inactivated SARS-CoV-2 virus) as “foreign.” This then induces an immune response against the already inactivated pathogen. 

CoronaVac is a COVID-19 vaccine made from inactivated SARS-CoV-2 virus.

The immune response to the inactivated pathogen ensures that the memory cells of our immune system know the “cheat codes” for the next time it is exposed to the pathogen we vaccinate against. Using these “cheat codes,” our bodies are guaranteed to win the fight against the pathogen for which it receives a vaccine that we may naturally be exposed to at a later time.

Inactivating the SARS-CoV-2 virus

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As we’ve just discussed, vaccines train our immune systems to fight off diseases caused by pathogens like bacteria and viruses. CoronaVac, an inactivated vaccine, uses a killed version of the SARS-CoV-2 virus. The infectious agent (in this case, the SARS-CoV-2 virus) is grown in the laboratory, and then inactivated or rendered uninfectious using chemicals.

inactivated vaccines syringe cartoon

An inactivated vaccine contains pathogens that are rendered uninfectious using heat/chemicals.  Source: The Shared Microscope on Instagram.

Since the virus is inactivated, it can no longer cause infection or even replicate when injected into a human.  For this reason, this type of vaccine is also safe for use in an immunodeficient person. 

Once injected with CoronaVac’s vaccine, our immune cells will be able to detect these inactivated, free-floating SARS-CoV-2 viral particles. Recognizing the viral particles as “foreign,” the immune cells will mount an immune response to break down and neutralize the inactivated SARS-CoV-2. This immune response will establish immunity, and thereby help our bodies eliminate SARS-CoV-2 when naturally exposed at a later date.

Since the viruses in this vaccine are whole inactivated viruses, the vaccine may not be capable of evoking a very robust immune response. The CoronaVac may therefore require the recipient to take booster shots to ensure a robust immune response. It should also be noted that, because the virus is inactivated, a higher vaccine dose is usually required for optimal immunity.

CoronaVac Clinical Trials

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Following success in preclinical research done on animal models, CoronaVac commenced clinical trials in Spring of 2020.  The CoronaVac vaccine is one of several Chinese companies that have gotten approval to continue on to human trials. If human trials are successful, Sinovac Biotech is on track to make 100 million vaccine doses per year.

Sinovac started human trials in April to test the safety of the CoronaVac vaccine. In June 2020, Sinovac announced the results of their Phase I/II clinical trials. In these trials, 743 healthy volunteers aged 18 to 59 years old received the experimental CoronaVac vaccine. Of the 743, 143 volunteers were in Phase I studies and 600 volunteers in Phase II. Taken together, the results of the trials showed that there were no severe adverse events reported in either Phase I or in Phase II clinical trials. Sinovac also announced that the results of their Phase II trials showed that the vaccine was able to produce neutralizing antibodies 14 days after vaccination. The vaccine therefore looks promising as a candidate that will help us control the COVID-19 pandemic.

Since Sinovac completed the Phase I/II studies, they could go ahead into Phase III trials. One of the biggest obstacles that the company was facing, for the Phase III trials, was the lack of COVID-19 transmission in China. For this reason, Sinovac applied for approval to carry out their trials internationally. 

Sinovac Biotech is now collaborating with Instituto Butantan in Brazil to conduct Phase III clinical trials. They have as of July 03, 2020 received approval for phase 3 trials in Brazil. The trial in Brazil is pivotal to support the licensure of this vaccine. Nearly 9,000 healthcare professionals working frontline to manage the COVID-19 crisis are set to receive this experimental vaccine developed by Sinovac Biotech.  

When Will CoronaVac or Another COVID-19 Vaccine be Approved for Use?

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Currently, the hope is that, as early as Fall 2020, we will hear more about the safety and efficacy of the CoronaVac vaccine and the other vaccines in Phase III clinical trials (including Moderna and Oxford). If Phase III clinical trials go well, we could see these vaccines hit the commercial market shortly thereafter.

#COVID19 vaccine developers could have Phase 3 results ready as early as this fall, with #vaccines being authorized for use shortly thereafter. @TheSharedScope

It should be noted, though, that the development of one or even several vaccines is not the only answer to ending the pandemic. What we need is a multifaceted approach to ensure a vaccine is developed and delivered to the majority of the population worldwide, and until we can do that, social distancing rules must be followed and testing and contact tracing must continue. 


This post was written by Nidhi Parekh of The Shared Microscope. Check out The Shared Microscope on TwitterFacebook, or Instagram for more fun and informative illustrations of different scientific concepts.

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