science

Covid vaccines: what are the implications of new variants of virus?


In common with others, the virus that causes Covid-19 mutates as it spreads. Most mutations have little or no effect, but some can change the behaviour of the virus. Mutations in a variant found in the UK in September has helped the virus spread more easily and potentially more dangerously. Further changes in variants that emerged in South Africa and Brazil may help the virus resist antibodies induced by vaccines and Covid infections from the first wave.

Why would the vaccines be updated?
If scientists spot new variants of coronavirus that are resistant to current vaccines then the vaccines will need to be redesigned to make them effective again. The more people who have immunity, either through vaccination or past infection, the more evolutionary pressure there is on the virus to evolve around that immunity. And when there’s lot of virus around, as there is now, there are more opportunities for resistant variants to emerge.


How are vaccines redesigned?
It depends on the vaccine. There are two vaccines being rolled out in the UK at the moment, one from Oxford/AstraZeneca, the other from Pfizer/BioNTech. Both contain genetic instructions for the spike protein which covers the surface of the virus. When the immune system encounters the spike protein it raises an army of antibody and T cells that is then primed to attack the virus should it come along. Updating the vaccine is not hard, at least conceptually: scientists simply replace the genetic code for the old spike protein with the code for the spike protein from the new variant.


How long does it take?
The vaccine can be redesigned on a computer within days. What takes more time is the manufacturing, testing and then large-scale production. Small batches of redesigned vaccine could be ready for testing within a month or two of the decision to update the formulation. Shots of the updated vaccine would then be tested in the laboratory to see whether they elicit the right immune response and do not raise any safety concerns. Regulators are in the process of deciding precisely what tests would be needed to make them confident an updated vaccine was safe and effective. It is highly unlikely they will require vaccines to go through a whole new round of clinical trials, just as seasonal flu shots are approved without such trials. As happened first time around, the updated vaccine could go into production while regulators pore over the safety and efficacy data, so that shots can be distributed as soon as the vaccine gets the green light. Though faster than updating flu vaccine, which is still grown in eggs, the whole process would still take months.

The Pfizer/BioNTech Covid jab is an mRNA vaccine. Essentially, mRNA is a molecule used by living cells to turn the gene sequences in DNA into the proteins that are the building blocks of all their fundamental structures. A segment of DNA gets copied (“transcribed”) into a piece of mRNA, which in turn gets “read” by the cell’s tools for synthesising proteins.

In the case of an mRNA vaccine, the virus’s mRNA is injected into the muscle, and our own cells then read it and synthesise the viral protein. The immune system reacts to these proteins – which can’t by themselves cause disease – just as if they’d been carried in on the whole virus. This generates a protective response that, studies suggest, lasts for some time.

The two first Covid-19 vaccines to announce phase 3 three trial results were mRNA-based. They were first off the blocks because, as soon as the genetic code of Sars-CoV-2 was known – it was published by the Chinese in January 2020 – companies that had been working on this technology were able to start producing the virus’s mRNA. Making conventional vaccines takes much longer.

Adam Finn, professor of paediatrics at the Bristol Children’s Vaccine Centre, University of Bristol

Would people need to be revaccinated?
Vaccinations programmes for Covid may need to mirror the annual flu vaccine programme, whereby the vaccine is modified each season to maximise its effectiveness. At the moment, the UK regulator believes there is no evidence that current vaccines will not work against the recently discovered new variants of coronavirus, but a strain known as 501Y.V2, which was first identified in South Africa, is causing concern because it is partially resistant to antibodies in people who caught Covid before. If surveillance shows that the variant, or others that emerge, are substantially resistant to current vaccines, then the vaccines will be updated. The new shots would then be given as soon as they are ready, with future updates happening annually or as-and-when new variants demand.



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