A vaccine against Covid-19 is urgently needed if we want to stop the spread of the virus and potentially prevent millions of further deaths. We are already one step closer to this goal.
We published early results from our clinical trial of the ChAdOx1 nCoV-19 vaccine (also known as AZD1222), designed by the University of Oxford and developed in partnership with AstraZeneca. Preliminary data indicate that it is safe and elicits a strong antibody response in all vaccinated volunteers, suggesting that an effective vaccine may be in place.
This test was the first time the vaccine was given to humans: 543 healthy adults aged 1
Preliminary data from the study clearly show that the vaccine elicits an antibody response within 28 days. This response is in a similar range to that of individuals who have recovered from Covid-19, providing encouragement that the vaccine will be able to protect the majority of people against infection.
Ten volunteers were given a second “booster” dose of the vaccine. This increases the response of the antibodies to even higher levels and 100% of the blood samples from this group show neutralizing activity against Covid-19 infection in the laboratory.
The vaccine also induces T cells that specifically recognize SARS-CoV-2, the virus that causes Covid-19. It is encouraging to see both antibodies and T-cell responses, as together this is the right type of immune response that can lead to protection against the virus. Importantly, the vaccine demonstrates an acceptable safety profile without severe side effects caused by the vaccine – ie no major side effects.
We were confident to test the vaccine in humans after promoting experiments with rhesus macaque mice and monkeys. They showed that the vaccine was safe and elicited a strong immune response. Significantly, vaccinated monkeys were protected from serious disease after being induced with a much higher dose of SARS-CoV-2 than humans would encounter through natural exposure.
How does the Covid-19 vaccine work?
Vaccines work by training the immune system to recognize and fight infectious agents (pathogens), such as bacteria and viruses. Vaccines do this by presenting to the immune system an easily recognizable part of a pathogen that the immune system remembers so that it can react quickly if it encounters the same pathogen in the future.
Most vaccines under development for SARS-CoV-2 – including this one – focus on the presentation of the thorn protein that adorns the surface of the virus. It is this protein that allows the virus into human cells by binding to a molecule on their surface called ACE2.
There is a wide range of approaches to vaccine design; ChAdOx1 nCoV-19 is what is known as a viral vector vaccine. To make this vaccine, particles from a different, harmless virus (called ChAdOx1) are loaded with the portion of SARS-CoV-2 DNA that instructs cells how to build the spike protein.
When these ChAdOx1 particles infect human cells, the coronavirus DNA is then “expressed”, building a spike protein for the immune system to respond. Important for the safety of the vaccine, the viral vector cannot replicate and cause a continuing infection.
The viral vector ChAdOx1 has been used to make eight vaccines, already in clinical trials for other human diseases, including Mers (Middle East Respiratory Syndrome), a coronavirus that is associated with SARS-CoV-2.
What happens next – The most important thing is to demonstrate that the vaccine is effective – that it leads to significantly lower (ideally zero) cases of Covid-19 in the vaccinated group ChAdOx1 nCoV-19 compared to the control group. The declining infection rate in the UK is an excellent result for the nation’s health, but it could compromise the ability to show this.
If there were no cases of Covid-19 in the group receiving the control vaccine, comparing this group with the vaccinated group would be meaningless. Intentionally infecting people with the virus may be possible in the future (after careful consideration of the ethical implications), but is not currently allowed.
For this reason, a second trial of approximately 10,000 people has been launched in the UK, focusing on health professionals, and further trials are being conducted in Brazil and South Africa, where infection rates are much higher. The extended study in the UK will include children and adults to evaluate the effectiveness of the vaccine in these age groups. Immune responses in people over the age of 70 are often lower than in younger adults.
It is essential to monitor the immune-induced vaccine for at least one year to assess whether booster injections will be needed and, if so, how often. My personal prediction – based on lowering antibody levels in individuals infected with other types of coronavirus, rather than data from the current vaccine trial – is that we may need annual boosters, similar to annual flu.
Finally, if the vaccine proves effective, it will require the rapid production of potentially billions of doses to provide the world. To facilitate this, AstraZeneca has already launched a large-scale vaccine production program aimed at hundreds of millions of doses, with delivery starting by the end of 2020. Vaccine agreements are being reached for low-income and middle-income countries, as well as to the United Kingdom, Europe and the United States.
This article was originally published in The Conversation by Rebecca Ashfield at Oxford University. Read the original article here.