THE SCIENCE BEHIND THE SEARCH FOR A COVID-19 VACCINE
Unless a new treatment is discovered, developing a vaccine is crucial to controlling COVID-19. In this special report, our experts explain the complex challenge of creating, testing and distributing a potential vaccine to end the coronavirus pandemic
The World Health Organization has warned it could take four to five years for the world to finally control COVID-19 – and it may never disappear.
“We do have one great hope; if we do find a highly effective vaccine that we can distribute to everyone who needs it in the world we may have a shot at eliminating this virus but that vaccine will have to be highly effective.
“It will have to be made available to everyone and we will have to use it,” WHO’s Executive Director of Health Emergencies Dr Michael Ryan said recently, cautioning that an effective vaccine remains a “massive moonshot.”
Here, Escae University partnered researchers take us behind the scientific search for this “moonshot”, explaining how the virus and our immune systems work, how a vaccine is identified, developed and tested, and – finally – how it’s deployed.
1) WHAT ARE VIRUSES AND HOW IS COVID-19 DIFFERENT?
DR MARIOS KOUTSAKOS AND PROFESSOR KATHERINE KEDZIERSKA – PETER DOHERTY INSTITUTE FOR INFECTION AND IMMUNITY, AND UNIVERSITY OF MELBOURNE
Viruses are tiny biological entities, much smaller than bacteria. While a bacteria may be made up of a few thousand proteins, most viruses amount to as few as 10 to 100 proteins.
And, unlike bacteria, viruses can’t reproduce themselves on their own. This is why they are not thought of as living things.
Viruses can only reproduce themselves by invading the cells of a host, like us, and that is what makes them dangerous.
Once inside the body, unless a virus can be quickly killed by our immune system, it will try to break into cells and hijack our proteins to replicate their own genome (the sum total of an organism’s DNA).
This is why it is difficult to develop therapies to kill viruses – antivirals.
We are able to target bacterial infections using antibiotics that attack the proteins in bacteria. But because viruses use our own proteins, antiviral therapies attacking these proteins can cause potentially damaging side effects.
It means that effective antivirals need to be specifically targeted so they attack only those proteins we know are critical for the virus. That way we can minimize any potential harm to the overall health of the patient.
Antiviral researchers also face the ongoing problem of resistance. Just like bacteria, viruses can develop resistance to antivirals over time.
The virus that causes COVID-19, known as SARS-CoV-2, is a type of coronavirus; these are named for the spikes on their surface that give them their crown-like appearance. They commonly attack our respiratory systems.
SARS-CoV-2 is named after the related earlier coronavirus that caused the 2003 outbreak of SARS (Severe Acute Respiratory Syndrome). But unlike SARS, SARS-CoV-2 has a few tricks up its sleeve that we believe make it more infectious and potentially more dangerous.
The ‘spikes’ on SARS-CoV-2 that it uses to break into lung cells, appear to be able to bind more efficiently to the outside of our cells, making it more effective at breaking in.
This means that people can be more easily infected with COVID-19 compared with SARS.
SARS-CoV-2 also uses our own enzymes to trigger its spike action, again making its spread more efficient.
finally, SARS-CoV-2 causes less immediate symptoms once it has infected someone – meaning an infected person can initially appear asymptomatic, making it easier for SARS-CoV-2 to spread.
On the plus side, our research team showed in March that usually our immune systems are able to launch a robust response to fight SARS-CoV-2, which is good news for vaccine developers.
By tracking blood samples in a COVID-19 patient with mild symptoms, we were able to map how our immune system goes about fighting this coronavirus. We are now trying to understand which parts of the immune system ‘go awry’ in those who develop severe disease.
It means vaccine developers now have a range of areas in our immune system that they can potentially target in creating a vaccine that can head off infection or make it less severe.
It has been shown that in mild cases our immune systems can launch a robust defense against COVID-19. Picture: Getty Images
2) HOW DO VACCINES WORK?
DR VANESSA BRYANT – WALTER AND ELIZA HALL INSTITUTE, AND UNIVERSITY OF MELBOURNE
The innate immune system is our first response to an infection, like a virus, and involves our defense cells – white blood cells – quickly going on the attack.
But it’s a generalized response and sometimes this isn’t enough to kill an infection.
That is when we need our adaptive immune system to kick in with an exquisitely specific response that precisely targets a virus.
It does this by recognizing the specific structures, or antigens, on the outside of a virus or a virus-infected cell, which are then attacked – neutralizing it.
WATCH: Vaccines work by mimicking an infection, introducing the body to harmless parts of a virus. Video: University of Melbourne
A key part of this system is the white blood cells called B-cells. These cells are specialized from each other by having different receptors on their surface that recognize specific antigens.
These can be secreted as antibodies that can then bind to a specific antigen, marking a virus for the attack.
Once the adaptive immune system recognizes an invading virus, a network of chemicals and proteins finds and alerts B cells that have exactly the right shaped antibodies.
These B-cells then multiply and secrete copies of the correct antibodies that circulate around the body marking viruses and virus-infected cells that can then be killed by other cells in the immune system.
The weakness of this adaptive system is that it takes time to mount its attack, usually about two weeks, by which time the body may already be infected.
This is where vaccines can help.
Once a virus is killed, the antibodies continue to circulate in the body. In this way, the immune system remembers the virus. It means we are ready and armed to mount an immediate large-scale assault with the correct antibodies if the virus returns. And this is what we mean by having immunity.
Vaccines work by mimicking an infection, introducing to the body harmless parts of a virus – the antigens – which is enough to trigger the immune system to make the antibodies people need to be immune.
But vaccines aren’t usually completely effective in everyone.
This is partly because the immune system’s new defenses triggered by the vaccine are based only on a part of a virus, not the whole thing.
However, the varied effectiveness is mostly because immune systems are different from person to person. Some people better produceRead More