How Bharat Biotech’s Covaxin vaccine works

Indian company Bharat Biotech has partnered with the National Institute of Virology and the Indian Medical Research Council to develop an inactivated coronavirus vaccine called Covaxin. India authorized the vaccine for emergency use on January 3, despite the lack of published Phase 3 data showing that the vaccine is safe and effective.

A vaccine made from coronavirus

Covaxin works by teaching the immune system to produce antibodies against the SARS-CoV-2 coronavirus. Antibodies bind to viral proteins, such as so-called peak proteins, which are on their surface.

To create Covaxin, Bharat Biotech used a sample of the coronavirus isolated by the National Institute of Virology in India.

Killing the Virus

As soon as the researchers produced large stocks of coronavirus, they immersed them in a chemical called beta-propiolactone. The compound deactivated coronaviruses by binding to its genes. Inactivated coronaviruses were no longer able to replicate. But its proteins, including the peak, remained intact.

The researchers then removed the inactivated viruses and mixed them with a small 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 more than a century. Jonas Salk used them to create his polio vaccine in the 1950s and they are the basis for vaccines against other diseases, including rabies and hepatitis A.

Requesting an immune response

As the coronaviruses in Covaxin are dead, they can be injected into the arm without causing Covid-19. Once inside the body, some of the inactivated viruses are swallowed up by a type of immune cell called an antigen-presenting cell.

The antigen-presenting cell separates the coronavirus and displays some of its fragments on its surface. A so-called auxiliary T cell can detect the fragment. If the fragment fits into one of its surface proteins, the T cell becomes activated and can help recruit other immune cells to respond to the vaccine.

Making Antibodies

Another type of immune cell, called a B cell, can also find the inactivated coronavirus. B cells have surface proteins in a wide variety of forms, and some may have the right shape to attach to the coronavirus. When a B cell is fixed, it can pull part or all of the virus inward and have fragments of coronavirus on its surface.

An auxiliary T cell activated against the coronavirus can cling to the same fragment. When this happens, cell B is also activated. It proliferates and releases antibodies that have the same shape as its surface proteins.

Stopping the virus

Once vaccinated with Covaxin, the immune system can respond to infection with live coronaviruses. B cells produce antibodies that stick to invaders. Antibodies that target the spike protein can prevent the virus from entering cells. Other types of antibodies can block the virus by other means.

Remembering the virus

Covaxin is being tested in two doses, administered four weeks apart.

If the Bharat Biotech Phase 3 clinical trial shows that Covaxin protects people against Covid-19, researchers will have to watch it for months to see how long this protection lasts. It is possible that the level of antibodies will drop, but the immune system also contains special cells called memory B cells, which can retain information about the coronavirus for years or even decades.

Vaccine Timeline

June 2020 Covaxin is the first coronavirus vaccine created in India to be approved for clinical trials.

July A Phase 1/2 clinical trial begins with 755 participants.

September The results of studies with monkeys and hamsters show that Covaxin offers protection against infections.

October, 23 The company announce a Phase 3 trial with up to 25,800 participants.

December The Covaxin phase 1/2 trial shows that the vaccine produces antibodies to the coronavirus without causing serious side effects.

December 22 Bharat Biotech announces a partnership with Ocugen, based in Pennsylvania, to develop Covaxin for the United States market.

January 3, 2021 The Indian government grants emergency authorization to Covaxin, although there is no release of Phase 3 data showing that the vaccine is safe and effective. The country also authorizes a vaccine made by Oxford University and AstraZeneca.

Sources: National Center for Biotechnology Information; Science; The Lancet; Lynda Coughlan, University of Maryland School of Medicine; Jenna Guthmiller, University of Chicago.

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