Coronavirus explained: How the '90 per cent effective' Covid-19 vaccine works

The vaccine uses a process that has never been approved for human use

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On Monday, drug firms Pfizer and BioNTech stunned the world by announcing they had developed a Covid-19 vaccine that was more than 90 per cent effective.

Few scientists believed that level of protection, which would put it on par with some childhood vaccines, would be possible that early on in the development of a vaccine against the coronavirus.

Many thought the first generation of immunisations would be around 50 to 60 per cent efficacious at best.

The stock market surged and experts around the world welcomed the news, which raised hopes the beginning of the end was now in sight after a year-long struggle against the pandemic.

However, many experts have said more information is still needed.

Pfizer's Covid vaccine is more than 90% effective

Pfizer's Covid vaccine is more than 90% effective

The companies have not yet shared data in a peer-reviewed journal. The trial is still ongoing and some have cautioned the vaccine’s efficacy could change over time.

Nevertheless, if the results hold up experts said the vaccine could help "bend the curve of the outbreak".

The vaccine has been developed using a process – mRNA technology – which has never been approved for human use.

So how does it work?

The National explains.

How do mRNA vaccines differ from more conventional ones?

All vaccines have the same goal: to trick the body into thinking it has had the virus.

Traditional vaccines essentially inject people with a dead, weakened, or part of a virus so the body makes antibodies against it, as it would in a natural infection.

But the process behind mRNA vaccines is completely different.

The m stands for messenger RNA.

They work by harnessing human cells to become their own miniature vaccine factories, by delivering genetic instructions that prompt the body to produce virus proteins – without exposing the body to it.

Once this happens, the immune system begins to build up protective antibodies to guard against infection.

What is the benefit of this approach?

The process of making vaccines can be slow.

Flu vaccines, for instance, are still grown in chicken eggs. That is a severe limitation when the world is fighting a pandemic, as it creates additional supply issues. They are also developed from live virus originally grown in a lab.

Experts say by contrast, mRNA vaccines can be designed on a computer in a matter of hours, making them cheaper to produce than traditional vaccines, and easily scalable.

"The advantage of RNA is that it takes you literally days to make a new vaccine," Drew Weissman, an immunologist at the University of Pennsylvania and an expert about mRNA vaccines, was quoted as saying in the Simthsonian Magazine.

When were mRNA vaccines first developed and why have they not been approved for use in humans yet?

The concept was first demonstrated in 1990, but the delivery often ended badly in animal experiments, inducing massive inflammation in mice.

However, scientists, who included Mr Weissman, eventually discovered how to dampen or remove this risk, paving the way for scientists to develop safe mRNA vaccines for humans.

Much of the work that has taken place in the field so far has focused on cancer, where they show promise.

But because the technology is fairly new and until now untested, there was no rush to get a mRNA vaccine to the market. The pandemic provided a new impetus.

Are there other mRNA vaccines in development for Covid-19?

Yes, an American company called Moderna is also developing a coronavirus vaccine using the same process. Scientists will be watching keenly to see if Moderna’s version is as successful.

There are more than 240 vaccines in development worldwide against Covid-19.

Most use a protein subunit. A viral vector is the second most popular vaccine, followed by the mRNA or DNA method, which both use the same technique. There are around 50 of these in development.

What other forms of Covid-19 vaccines are being trialled?

  • Live attenuated virus, which is a weakened version made by mutating the original virus
  • Inactivated virus, which is made by disabling the virus through radiation, chemicals or heat
  • A protein subunit, which contains one piece of a coronavirus antigen that cannot replicate and do harm
  • Virus-like particles, which resemble the virus in structure but do not contain its genetic material
  • Viral vectors, which contain instructions for the body to fight the virus