The quest to build immunity against the ravaging COVID-19 has been led by six vaccine developers including Johnson & Johnson, AstraZeneca, Novavax, Pfizer/BioNTech, Gamaleya, Moderna and Sinovac.
They all made it to the third phase of clinical trials in 2020 out 320 Covid-19 vaccine candidates in development but only two have been approved after demonstrating nearly 100 per cent efficacy.
Pfizer/BioNTech and Moderna are leading the vaccine race using the same technology: ribonucleic acid (RNA). Others have been developing their vaccine mostly through the viral vector approach which works by replacing non-essential viral genes with foreign genes of therapeutic interest.
Why are mRNA vaccines showing the most promise? How do they work and why are they safe?
How RNA works
Gavi, The Vaccine Alliance, the coordinator of COVAX in a breakdown of how the technology works explains that the RNA, closely related to DNA, is present in all living cells.
The strand of it called messenger RNA is a sequence of genetic code that tells cells what proteins to build so that they can function.
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To produce an RNA vaccine, scientists develop a synthetic version of some of the virus’ messenger RNA.
When this is injected into the human body, cells read it as an instruction to start building the proteins, including, in this case, Covid-19’s distinctive ‘spike’ protein.
The body then mounts an immune response by producing antibodies to fight the virus proteins made by our cells. This prepares the immune system to fight the real virus when encountered later on.
It is different from the way some other vaccines work, where a small part of the virus itself, or the whole virus (weakened or dead), is injected into the body to trigger an immune response.
Why is RNA vaccine most promising?
RNA vaccines hold the promise of being faster, cheaper, more adaptable and easier to mass-produce than other vaccines, mainly because they can be generated quickly.
The technology is based on a process of biochemical synthesis that involves fewer components and fewer steps than the more complex traditional methods, like using inactivated live viruses.
This means they are quicker to get into clinical trials and quicker to manufacture once the trials are completed in a matter of weeks and months.
Only a small amount of RNA needs to be delivered into the body’s cells, compared to the much larger micrograms of protein that are required for many other vaccines.
This means each individual vaccine dose should be cheaper to purchase, although it is dependent on the price set by pharmaceutical companies and the costs of delivery.
They could be more adaptable and easier to manufacture at scale. Also, the same RNA vaccine platform could be used to produce vaccines against different diseases – both known and emerging.
A manufacturing plant could, in theory, produce multiple vaccines using the platform, whereas other vaccines, such as MMR (measles, mumps, and rubella) and Ervebo (one of the Ebola vaccines), each require their own dedicated manufacturing plant.
Have there been any other RNA vaccines?
There are no other licensed RNA vaccines. Pfizer-BioNTech vaccine is the first.
However, researchers have been using the technology for a while, and people have been given RNA vaccines in clinical trials for other diseases, like cancer.
A major challenge in the past has been figuring out how to deliver the RNA vaccine into the cell so it survives since the human body naturally wants to destroy foreign RNA molecules.
This new use of RNA has only been made possible due to the enormous level of research funding and focus during the pandemic, which has allowed breakthroughs in new technologies.
When will the vaccines be available?
Pfizer-BioNTech promised to supply 50 million doses by the end of 2020 and around 1.3 billion by the end of 2021.
Moderna intended to provide the US government with 20 million doses by the end of 2020, and manufacture between 500 million and one billion doses globally throughout this year.
Are there limitations?
There are still many outstanding questions, for example how long immunity will last for, how effective the vaccines will be in different populations, and whether people can still transmit the disease to others if they’ve been immunised.
Although Pfizer-BioNTech and Moderna have reported high levels of vaccine efficacy in over 65-year-olds – one of the groups most at risk of serious illness.
In addition, many vaccines need to be refrigerated – usually around 2 to 8C – the Pfizer-BioNTech Covid-19 vaccine needs to be stored at least -70C, which could pose problems for transporting and storing it, particularly in low- and middle-income countries where refrigeration facilities may be limited.
The Moderna vaccine can be stored at fridge temperature for 30 days under 2 to 8C once delivered to healthcare facilities which is encouraging, but requires -20C for long-term storage and transportation.
COVAX has pledged to continue to invest efforts in a wider range of vaccines that show different characteristics, suitable for people of all ages and ethnic groups, including people with underlying health conditions, and able to be distributed and used in all settings around the globe.
