Moderna COVID-19 vaccine booster targets mutant strain

A third shot might be able to increase protection against the South African strain of COVID-19.

Biotech company Moderna has just announced the results of a study testing whether its COVID-19 vaccine could protect people against two quickly spreading strains of the coronavirus, one originating in the U.K. and the other in South Africa.

Based on those results, the vaccine appears to be just as effective against the U.K variant, but it’s less protective against the South African strain — so the company has developed a COVID-19 vaccine booster shot to target the new strain.

Tracking Coronavirus Mutations

As a virus spreads, its genetic code will occasionally undergo minor mutations. When we spot a version of the virus with a unique set of mutations, we call it a new strain or variant.

This is normal, so the emergence of new coronavirus strains is neither a surprise nor immediate cause for concern.

“New strains of the SARS-CoV-2 virus are detected every week,” Stuart Ray, a COVID-19 expert at Johns Hopkins University, said in December. “Most come and go — some persist but don’t become more common; some increase in the population for a while, and then fizzle out.”

However, the U.K. and South African strains neither flatlined nor fizzled — they both became more prevalent as time passed. That is cause for concern because it suggests that the strains might be more contagious (and recent studies have supported that theory).

The location of many of the mutations in the strains is also troubling.

The U.K. strain has eight mutations in the part of the virus targeted by all of the current COVID-19 vaccines (the spike protein), while the South African strain has 10 spike protein mutations.

Moderna’s COVID-19 Vaccine Booster

To find out whether those mutations would affect the vaccine’s efficacy, Moderna introduced the new variants to blood serum collected from eight vaccinated people, as well as non-human primates.

When mixed with the U.K. variant, vaccinated serum neutralized the viruses as well as the original strains, suggesting that the vaccine will be just as effective at protecting against it.

However, the neutralizing antibodies were six times less effective when Moderna tested the South African strain. Fortunately, because the vaccine produces such a strong immune response, the company said the vaccine should still be protective, but immunity against the South African strain might not be as long-lasting.

I think of it as an insurance policy.

Tal Zaks

Rather than wait and hope for the best, Moderna has already developed a COVID-19 vaccine booster designed to protect against the South African strain specifically.

“Out of an abundance of caution and leveraging the flexibility of our mRNA platform,” Moderna CEO Stéphane Bancel said in a press release, “we are advancing an emerging variant booster candidate against the variant first identified in the Republic of South Africa into the clinic to determine if it will be more effective to boost titers against this and potentially future variants.”

Preparing for the South African Strain

Bancel told the Financial Times that a few thousand already vaccinated people will receive a COVID-19 vaccine booster shot during this trial.

In some cases, this will be the version designed to protect against the South African strain specifically, while other people will just receive a third dose of the original vaccine to see if that’s enough to make up for the difference.

The approval process for a COVID-19 vaccine booster is expected to be far easier than the one for a brand new vaccine — rather than proving its ability to prevent infections all over again, Moderna will likely just need to show that it increases antibody levels sufficiently.

Whether a booster will even be necessary is still unknown, but as Moderna’s CMO Tal Zaks told the New York Times, it can’t hurt to have one ready.

“We’re doing it today to be ahead of the curve, should we need to,” he said. “I think of it as an insurance policy.”

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