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EXPLAINED: How 'Beta Testing' Of Oxford-AstraZeneca Covid Vaccine Can Up Game Against Variant

Representational image.

Representational image.

Trial of a new version of the Oxford-AstraZeneca vaccine represents the next steps in efforts to beat back new variants of the novel coronavirus

A new version of the Oxford-AstraZeneca vaccine, which is being made in India by the Serum Institute under the name Covishield and is the mainstay of the country’s vaccination drive, has been designed to counter the Beta variant of the novel coronavirus that was first seen in South Africa. Here’s why the trial is significant for everything from booster doses and mixing of shots.

Why Is A New Version Of The AstraZeneca Vaccine Being Trialled?

When the UK became the first country to okay the Oxford-AstraZeneca vaccine, in December last year, many of the variants that are driving infections today were absent or yet to be identified. But the emergence of variants gave rise to questions regarding the efficacy of vaccines even as countries pushed ahead with their Covid-19 inoculation drives.

As experts went to study the impact of the approved shots against the new variants, it was found that while new variants can have the ability to escape neutralising antibodies, vaccines do provide a level of safety against serious infection.

Authorities in South Africa, however, said they would not use the Oxford-AstraZeneca vaccine doses obtained by them as it was not effective against the Beta variant of the novel coronavirus that was first identified in that country. The new version of the Oxford-AstraZeneca vaccine is designed to blunt this Beta variant.

How Is The Vaccine Different From The Earlier Shot?

The Oxford-AstraZeneca dose that is now being used around the world has the clinical name AZD1222 and is built on the viral vector platform. That is, it uses a harmless virus — in this case a chimpanzee adenovirus — to insert a piece of the novel coronavirus’s spike protein into our body, which in turn prompts an immune reaction and trains the immune system to ward off any future attacks by the virus.

The new version of the vaccine is called AZD2816 and, according to AstraZeneca, “has been built using the same adenoviral vector platform” as the original vaccine. However, the spike protein that it will introduce to the human immune system is based on the Beta, or B.1.351, variant. However, “these modifications are only minor and in all other ways the two vaccines are the same,” AstraZeneca said.

“The Beta variant vaccine contains 10 changes across the spike protein, many of which are also seen in other variants of concern, and which lead to effects such as, reduced ability of antibodies induced against the original virus to block cell entry, increased infectivity compared to the original virus, reduced sensitivity of neutralising antibodies to the original virus,” the company added.

Beta has been classified as a variant of concern by the World Health Organisation (WHO) but it is the Delta variant that has triggered the most prominent surges in recent months, including in India. Experts say that the vaccines currently being used do provide some protection against the Delta as well as the Delta-plus variant that has now emerged.

Will The New Version Act As A Booster Dose?

It is evident now that success in the future battles of the pandemic will depend on how well we can combat newly emerging variants. It will be important to have vaccines that can blunt the impact of such variants. To that extent, the new Oxford-AstraZeneca vaccine can serve as a booster shot against future variants.

“It is important we continue to stay ahead of genetically distinct variants of the coronavirus. AZD2816 should help broaden individuals’ immune response against emerging variants of concern. Initiating the Phase II/III trial for AZD2816 means we can be prepared should a variant vaccine be required in the future,” said Mene Pangalos, a top official at Oxford-AstraZeneca.

Data from the trial is expected to come in later this year and the makers will seek approval for the vaccine as a “next-generation booster” shot.

What About Mixing Vaccine Doses?

The 2,250 participants in the trial that is being held at sites across the UK, South Africa, Brazil and Poland, will include those who have previously been fully vaccinated with two doses of AZD1222 or an mRNA vaccine, at least three months after their last injection. This detail is interesting as it opens up the possibility of the mixing of doses, something that experts have said should present no problems, although caution has been urged against implementing it in vaccination programmes in the absence of sufficient data.

The Pfizer-BioNTech and Moderna vaccines, which are the chief constituents of inoculation campaigns in advanced countries, are both mRNA vaccines. Studies that show vaccine doses can be mixed with no adverse effects will allow governments to be more flexible in vaccinating their populations as countries scramble to deal with supply issues.

The AZD2816 trial will also see the vaccine being mixed with the original AZD1222 in individuals who have not been vaccinated before.

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