How COVID vaccines are modified and how easy it would be to update them if the pathogen becomes resistant

Cómo se modifican las vacunas COVID y qué tan fácil sería actualizarlas si el patógeno se vuelve resistente

It is a fear that is on the minds of many.

That after a year of pandemic and a full-speed race to produce and distribute vaccines, suddenly a variant of coronavirus mutates so much that it becomes resistant to treatments.

It is the fear that exists after emerging variants such as those of UK, South Africa or Brazil, which spread rapidly in other countries.

The main manufacturers assure that their compounds will continue to work against these new mutations, but it has already been known that these vaccines lose some effectiveness before the South African mutation.

In recent days it became public that the vaccine from the University of Oxford and AstraZeneca protected less against moderate cases of covid disease in the South African variant, although it is small studies and for now it appears that the doses would continue to protect against severe cases and hospitalizations.

A few weeks ago, on the other hand, the American manufacturer Moderna had already announced that it would adapt its compound against this mutation.

In short, it is a scenario that scientists do not rule out: that the vaccines we havelose some effectiveness before the new variants.

However, updating or modifying a vaccine it’s not something new And it is done every year with the seasonal flu.


How much does the coronavirus have to mutate to become resistant?

Viruses constantly mutate and the current coronavirus has already done it several times since it was first detected in Wuhan.

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But scientists are concerned when the virus mutates so much that it causes the vaccines that were originally designed to lose partial or considerable efficacy, as the South African variant appears to be happening in early studies.

“To correct or update a vaccine, even if a new variant is more resistant, it must be verified that this vaccine is no longer significantly effective against the new version of the virus“Julian Tang, professor of virology at the University of Leicester in the United Kingdom, explains to BBC Mundo.

Coronavirus test in Brazil.

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For a virus to significantly reduce the effectiveness of a vaccine, it must mutate considerably.

In other words, if a virus changes and makes vaccines less effective, that does not mean that they do not continue to work with a considerable degree of effectiveness.

And it is quite unusual for a virus to mutate. so radical as to completely circumvent the protection of a vaccine.

“Viruses must maintain a certain shape to continue infecting cells. They can’t change much else. It is the job of the manufacturers to monitor the mutations and decide if they deserve to modify the vaccine “, says the expert.

The great danger today, Tang explains, is that if a mutation suddenly disables the millions of vaccines that are being distributed, this would interrupt global immunization and discard what was produced, although it is still too early to assume this scenario.

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How are vaccines modified and how easy is it?

How to modify a vaccine depends on your design and the technique you use.

In the case of vaccines based on the messenger RNA (mRNA) molecule, such as that from Pfizer, or on viral vectors, such as that from the University of Oxford, the update would be completed quite quickly, in one or a few weeks.

This is because “it is only necessary to update the fragment of the genetic code of the virus that contains the new mutation”, explains to BBC Mundo José Manuel Bautista, professor of the Department of Biochemistry and Molecular Biology at the Complutense University of Madrid, in Spain.

Professor Andy Pollard of the University of Oxford has already confirmed that his team is working on updating their vaccine to make it more effective against emerging mutations and hopes to have it ready by next fall.

“Updating a new vaccine is very, very fast because it basically consists of replacing the genetic sequence present in the so-called spike protein of the virus,” said Pollard.

Oxford and AstraZeneca vaccine.

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In the case of the Oxford and AstraZeneca vaccine, it would take a week or a few weeks to change.

But this process would take a few more months for vaccines that use inactivated viruses or protein subunits, as would be the case with the Chinese Coronavac vaccine and the American Novavax, respectively.

In these cases, “you first need to grow the virus or its protein in a laboratory and then purify and inactivate it to become a large-scale vaccine, which takes time,” Tang says.

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In any case, Dr. Andrew Badley, professor of molecular medicine at the Mayo Clinic in the United States, assures that “modifying a vaccine is much easier than creating one from scratch, but that it is not a trivial exercise and requires new checks of safety and immunological effectiveness ”.

Scientist analyzing samples in a laboratory.

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Vaccines based on inactive viral vectors take longer to update.

Experience with the flu

In recent months, we have heard more and more sectors of the scientific community pointing to the likelihood of the coronavirus becoming endemic, like the flu.

That might require vaccines to be updated every so often, but it’s something where scientists already have experience.

“Every year the circulating variants of the flu around the world are analyzed, which do not always coincide in the same hemisphere or continent. So, each country prepares specific vaccines for these variants. Something similar would happen with the coronavirus if that is the case, ”explains Bautista.

“The annual flu vaccine uses the virus subunit technique, like Novavax’s, and takes about six months to update and produce each year,” Tang says.

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