How does Oxford vaccine candidate work?

A Covid-19 vaccine that is being developed by University of Oxford and drugmaker AstraZeneca, is showing positive results in early human trials. The results published on Monday indicates that the vaccine triggers an immune response.

The Covid-19 virus (SARS-CoV-2), has spikes on its surface. So, when a person is infected, these spikes, known as the 'spike protein', allow the virus to penetrate cells and, thereafter, multiply.

The Oxford and AstraZeneca vaccine candidate is a non-replicating viral vector vaccine. It aims to develop the body's immunity to this spike antigen. The idea is to create antibodies to combat this spiked surface so that the virus cannot penetrate the cells.

The vaccine uses a weakened version of a common cold virus (adenovirus) to carry the code, to make the spike protein. This virus infects chimpanzees but for the vaccine, it is genetically programmed so that it cannot replicate in humans. The adenovirus can enter the cell and activate the code to generate only the spike protein. It is expected that the body's immune system will recognize the spike protein as a potentially harmful foreign substance, and begin to build antibodies against it.

Once immunity is built, if it tries to infect the body the antibodies will attack the real virus, reports the Indian Express.

What do the latest results mean?

The early findings from the vaccine's phase I / II trials, published in The Lancet, gave some hope by demonstrating that the vaccine was not only healthy but also seemed to build up an immune response among participants. For one, it was found that the injection with the vaccine led participants to build up antibodies that were neutralized. Another beneficial factor was that it raised the number of T cells — a type of white blood cell that protects the body from infections and cancer cells, and is involved in the elimination of infected cells.

A single dose of the vaccine was effective and showed an increase in antibodies specifically against the spike protein by 28 days. Neutralising antibody responses were detected in 32 of 35 participants studied after a single dose, and in all nine participants assessed after they were administered a second, booster dose.

The vaccine showed mild to moderate adverse reactions, including pain, feverish feelings, chills, muscle aches, headaches and malaise. The effects were reduced using prophylactic paracetamol, according to the study.

How significant is this?

Although the findings sound positive, it is important to note that these data come from scientific early-stage trials. Such results cannot answer issues such as how long the antibodies will remain in the body, which is a significant element in deciding how safe the vaccine will be. This will require data from larger phase III trials.

What happens next?

Oxford and AstraZeneca have already begun phase III trials in Brazil, recruiting 5,000 volunteers worldwide. A similar trial is expected to be underway in South Africa as well.
Meanwhile, India's Serum Institute, which has been linked to Oxford and AstraZeneca, aims to mass-produce the vaccine in the next three months after it earns a manufacturing license. The company is expected to manufacture the vaccine for countries with low and middle incomes.

However, Serum will have to conduct phase III trials in India before the vaccine can be launched. So far, the firm has received permission to manufacture certain doses for testing purposes, said a senior government official. "We will be applying for the licensure trials to the Indian regulator in a week's time. As soon as they grant us permission, we will begin with the trials for the vaccine in India," said Adar Poonawalla, CEO of Serum Institute.