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EXPLAINED: Alpha To Delta, One Shot To Beat Them All. Why Multivariant Jabs Could Be Future Of Covid Fight

The vaccine being tested in the UK has been developed by the US-based biotech company Gritstone. (File photo)

The vaccine being tested in the UK has been developed by the US-based biotech company Gritstone. (File photo)

What if a single vaccine could boost protection against multiple variants of the novel coronavirus? One such candidate is being trialled in the UK

New and emerging variants of the novel coronavirus are seen as being able to dodge antibodies acquired either through vaccination or prior infection. Which is why many countries are now providing booster shots of Covid-19 vaccines. While updated vaccines and additional shots are an option to counter potential future outbreaks — much like how existing vaccines are updated against the seasonal influenza — a single jab that is targeted towards multiple variants can offer a more convenient and long-lasting solution against the novel coronavirus. The test of one such vaccine was recently announced in the UK. Here’s what you need to know.

What Is A Multivariant Vaccine?

Several countries around the world, including the US, UK, Israel, France, Germany, have started rolling out booster shots for their vaccinated populations as health authorities fear that newer variants of the novel coronavirus can blunt the protection provided by the existing vaccines. Manufacturers across the world are themselves looking to update their doses to counter newer variants given that the current vaccines were developed in the early days of the pandemic, which means they are designed to counter strains that are no longer prevalent.

Scientists and health experts have pointed out that any vaccine that is being used now provides sufficient protection against severe infection and hospitalisation and breakthrough cases — where people contract Covid-19 after having received their full vaccine dose — are generally associated with mild or asymptomatic infection. But given the persisting pandemic and the propensity of the novel coronavirus to mutate, there are worries that newer variants could seed fresh surges of infection, as was seen with the Delta variant in the US.

The solution is to vaccinate as many people as quickly as possible, but with immunity provided by vaccines, or infection, seen to decline eventually, booster shots are being pushed as the answer against future waves of Covid-19. But booster shots are not qualitatively different from the primary doses and multiple jabs come with the risk of adverse reactions. But what if a vaccine could be created that could counter existing and future variants of the novel coronavirus? Enter multivariant vaccines, which are designed to expand on how existing vaccines target the virus.

How Does It Work?

Most of the existing vaccines target what is known as the spike protein of the novel coronavirus, which are the crown-like structures on its surface that give the virus its name. The spike protein, which the virus uses to invade and latch on to human cells, presents an easy target for researchers and current vaccines have been designed to train the immune system to identify and attack this component of the virus. However, most of the variants that have shown an ability to escape immunity conferred by vaccines or infection express key changes in this spike protein.

But Gritstone, the US-based company that is working on the multivariant vaccine — called GRT-R910 — says that its formulation targets “both the spike and non-spike proteins".

“Since viral surface proteins like the spike protein are evolving and sometimes partially evading vaccine-induced immunity, we designed GRT-R910 to have broad therapeutic potential against a wide array of Sars-CoV-2 variants by also delivering highly conserved viral proteins that may be less prone to genetic variation in the virus," said Andrew Allen, CEO of Gritstone.

The Gritstone vaccine is being described as a second-generation vaccine that is intended to “boost and expand the immunogenicity of first-generation Covid-19 vaccines".

“Our hypothesis is that a different vaccine such as GRT-R910 might complement the primary immune response from pre-existing vaccination with a first generation Covid vaccine in such a way that it would provide more benefit than an additional dose of the same vaccine," added Allen.

For example, the trial currently underway in the UK — involving a group of 20 people aged 60 years and above — “will explore the ability of GRT-R910 to boost and expand the immunogenicity" of Oxford-AstraZeneca’s first-generation vaccine, which is being used in India under the brand name Covishield.

While Covishield is a viral vector vaccine, GRT-R910 is based on the self-amplifying RNA platform.

What Is The saRNA Platform?

The unprecedented Covid-19 pandemic brought to the fore several solutions and medical technologies as experts and governments pursued accelerated timelines for the roll out of therapies and vaccines. One such platform, which had never been used before, was of the mRNA vaccine, among the first to be rolled out against the novel coronavirus. These vaccines — of which the Pfizer-BioNTech and Moderna jabs are prominent examples — work by showing the immune system a key piece of genetic information (in this case, that for Sars-CoV-2’s spike protein) in order to train it to identify and attack the virus.

Unlike the more traditional vaccines, they do not contain any actual pieces of the novel coronavirus and are hence considered to be safer and relatively easier to manufacture. But an absence of any actual components of the virus also means that their effect is considered to weaken over time. An saRNA vaccine works in the same way as the mRNA — the ‘m’ stands for ‘messenger’, since the vaccine carries instruction for the immune system itself to prepare the spike protein — except that it also carries other genetic information of the virus that allows augmented production of the spike protein, which contributes in turn to a stronger immune response even at lower doses.

Who Is Holding Trials? When Will The Vaccine Be Ready?

The trial for the Gritstone vaccine is being held in UK in collaboration with the University of Manchester and Manchester University NHS Foundation Trust and will initially recruit 20 volunteers over the age of 60. The results are expected to be released in the first quarter of 2022.

Gritstone said that the trial will “examine dose, safety, tolerability, and immunogenicity of GRT-R910 at two dose levels at least 4 months after the second administration of their initial vaccine". The vaccine is also being studied in a Phase 1 study in the US.

“Though the vaccine is being trialled in the over 60s, future studies will also examine its efficacy in other-vulnerable populations. If successful, we feel it has the potential to have play a significant role in the battle against Covid-19," said Prof. Andrew Ustianowski, chief investigator for the study.

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first published:September 27, 2021, 14:53 IST