LONDON: After China’s health authorities have approved a Covid vaccine from state-owned Sinopharm for general use on the population, the question is how the Sinopharm vaccine works to combat the deadly virus?
In early 2020, the Beijing Institute of Biological Products created an inactivated coronavirus vaccine called BBIBP-CorV. It was later put into clinical trials by the state-owned Chinese company Sinopharm. China approved the vaccine on Thursday, and the vaccine is also in use in Bahrain and the UAE, according to a report in Sky News Arabia.
BBIBP-CorV works by teaching the immune system to make antibodies against the SARS-CoV-2 coronavirus. The antibodies attach to viral proteins, such as the so-called spike proteins that stud its surface.
To create BBIBP-CorV, the Beijing Institute researchers obtained three variants of the coronavirus from patients in Chinese hospitals. They picked one of the variants because it was able to multiply quickly in monkey kidney cells grown in bioreactor tanks.
Once the researchers produced large stocks of the coronaviruses, they doused them with a chemical called beta-propiolactone. The compound disabled the coronaviruses by bonding to their genes. The inactivated coronaviruses could no longer replicate. But their proteins, including spike, remained intact.
The researchers then drew off the inactivated viruses and mixed them with a tiny amount of an aluminium-based compound called an adjuvant. Adjuvants stimulate the immune system to boost its response to a vaccine.
Inactivated viruses have been used for over a century. Jonas Salk used them to create his polio vaccine in the 1950s, and they’re the bases for vaccines against other diseases including rabies and hepatitis A.
Because the coronaviruses in BBIBP-CorV 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 tears the coronavirus apart and displays some of its fragments on its surface.
A so-called helper T cell may 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.
Another type of immune cell, called a B cell, may also encounter the inactivated coronavirus. B cells have surface proteins in a huge variety of shapes, and a few might have the right shape to latch onto the coronavirus. When a B cell locks on, it can pull part or all of the virus inside and present coronavirus fragments on its surface.
A helper T cell activated against the coronavirus can latch onto the same fragment. When that happens, the B cell gets activated, too. It proliferates and pours out antibodies that have the same shape as their surface proteins.
Once vaccinated with BBIBP-CorV, the immune system can respond to an infection of live coronaviruses. B cells produce antibodies that stick to the invaders.
Antibodies that target the spike protein can prevent the virus from entering cells. Other kinds of antibodies may block the virus by other means.
Sinopharm’s clinical trials have demonstrated that BBIBP-CorV can protect people against Covid-19. But no one can yet say how long that protection lasts.
It’s possible that the level of antibodies drops over the course of months. But the immune system also contains special cells called memory B cells that might retain information about the coronavirus for years or even decades.