How the Sinovac Vaccine Works
Private Chinese company Sinovac developed a coronavirus vaccine called CoronaVac. On December 23, Brazilian researchers announced that the vaccine was over 50 percent effective. Full details of Sinovac's Phase 3 trials are expected in early January.
A coronavirus vaccine
CoronaVac teaches the immune system to produce antibodies against the SARS-CoV-2 coronavirus. The antibodies bind to viral proteins, such as the so-called spike proteins, which examine their surface.
To develop CoronaVac, Sinovac researchers first received samples of the coronavirus from patients in China, Great Britain, Italy, Spain and Switzerland. A sample from China ultimately served as the basis for the vaccine.
Kill the virus
The researchers grew large stocks of the coronavirus in monkey kidney cells. Then they doused the viruses with a chemical called beta-propiolactone. The compound deactivated the coronaviruses by binding to their genes. The inactivated corona viruses could no longer replicate. But their proteins, including the tip, remained intact.
The researchers then peeled off the inactivated viruses and mixed them with a tiny amount of an aluminum-based compound called an adjuvant. Adjuvants stimulate the immune system to increase its response to a vaccine.
Inactivated viruses have been used for over a century. Jonas Salk used them to make his polio vaccine in the 1950s and they are the basis for vaccines against other diseases such as rabies and hepatitis A.
Invitation to the immune response
Since the coronaviruses in CoronaVac are dead, they can be injected into the arm without causing Covid-19. In the body, some of the inactivated viruses are swallowed by a type of immune cell called an antigen-presenting cell.
Present
Virus protein
Fragments
Present
Virus protein
Fragments
Present
Virus protein
Fragments
The antigen presenting cell tears up the coronavirus and shows some of its fragments on its surface. A so-called helper T cell can detect the fragment. When the fragment fits into one of its surface proteins, the T cell is activated and can help recruit other immune cells to respond to the vaccine.
Make antibodies
Another type of immune cell called a B cell can also encounter the inactivated coronavirus. B cells have surface proteins in a variety of shapes, and some may be the right shape to attach to the coronavirus. When a B-cell locks into place, it can draw in some or all of the virus and present coronavirus fragments on its surface.
A helper T cell activated against the coronavirus can bind to the same fragment. In this case, the B cell is also activated. It multiplies and releases antibodies that are the same shape as their surface proteins.
Matching
Surface proteins
Matching
Surface proteins
Matching
Surface proteins
Matching
Surface proteins
Matching
Surface proteins
Matching
Surface proteins
Matching
surface
Proteins
Matching
surface
Proteins
Matching
surface
Proteins
Matching
Surface proteins
Matching
Surface proteins
Matching
Surface proteins
Stop the virus
After vaccination with CoronaVac, the immune system can react to an infection with live coronaviruses. B cells produce antibodies that adhere to the invaders. Antibodies that target the spike protein can prevent the virus from entering cells. Other types of antibodies can block the virus in different ways.
Memory of the virus
While CoronaVac can offer some protection against Covid-19, no one can yet say how long this protection will last. It is possible that antibody levels may drop over the months. The immune system also contains special cells, so-called memory B cells, that can store information about the coronavirus for years or even decades.
Vaccination schedule
January 2020 Sinovac begins development of an inactivated vaccine against the coronavirus.
Sinovac engineers work with monkey kidney cells.Nicolas Asfouri / Agence France-Presse
June No serious side effects were found in phase 1/2 studies in 743 volunteers.
July Sinovac is starting a phase 3 trial in Brazil, followed by others in Indonesia and Turkey. Reuters reports that the Chinese government has issued the Sinovac vaccine emergency approval for limited use.
A dose of CoronaVac in Turkey.Emrah Gurel / Associated Press
October Authorities in east China's Jiaxing city have announced that they are releasing CoronaVac to people at relatively high risk, including medical workers, port inspectors and public service workers.
October 19th Officials in Brazil say Sinovac is the safest of five vaccines they are testing in Phase 3 studies.
November Sinovac publishes the details of its phase 1/2 study in a medical journal, which shows a comparatively modest production of antibodies. Only a phase 3 study will show whether this is enough to protect people from Covid-19.
November 19th The Brazilian government announces that it suspended the country's Sinovac trial the previous month because of an adverse event. The details of the break were hazy and raised suspicions that politics was involved. The trial was allowed to continue two days after the announcement. Enough cases of Covid-19 were registered in the Brazilian study for researchers to determine the effectiveness of Sinovac. They expect to publish their results by December 23rd.
Officials in Brazil hold boxes from a shipment of the vaccine.Alexandre Schneider / Getty Images
December Sinovac expects to produce 300 million cans in 2020 and increase capacity to an annual production of 600 million cans.
23rd of December Brazilian researchers announce that CoronaVac has an effectiveness of over 50 percent.
Sources: National Center for Information on Biotechnology; Science; The lancet; Lynda Coughlan, University of Maryland Medical School; Jenna Guthmiller, University of Chicago.
Comments are closed.